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عینک eyewear - Vision Disorders اختلالات بینائی

ابزار وبمستر

ابزار وبمستر

عینک ، سلامتی چشم ، لنز ، راه های پیشگیری ، کنترل و درمان بیماریهای چشمی

Nearsightedness is a very common vision condition affecting nearly 30 percent of the U.S. population. Some research supports the theory that nearsightedness is hereditary. There is also growing evidence that it is influenced by the visual stress of too much close work.

Generally, nearsightedness first occurs in school-age children. Because the eye continues to grow during childhood, it typically progresses until about age 20. However, nearsightedness may also develop in adults due to visual stress or health conditions such as diabetes.

 If one or both parents are nearsighted, there is an increased chance their children will be nearsighted.

The exact cause of nearsightedness is unknown, but two factors may be primarily responsible for its development:

    

  • heredity
  • visual stress

Visual stress (sometimes called 'Meares-Irlen Syndrome' or 'Scotopic Sensitivity Syndrome') is the experience of unpleasant visual symptoms when reading, especially for prolonged periods. Symptoms include illusions of shape, movement and colour in the text, distortions of the print, loss of print clarity, and general visual irritation. Visual stress can also cause sore eyes, headaches, frequent loss of place when reading, and impaired comprehension.     

           

Visual stress can have an adverse effect on the development of reading skills, especially reading fluency - i.e. the ability to recognise words quickly and to read longer passages text of text in a smooth and efficient way so that good comprehension is maintained. Visual stress makes reading an unpleasant and irritating activity that children will tend to avoid as much as possible. Research has shown that 15 - 20% of people suffer visual stress to some extent, and they also tend to be hypersensitive to fluorescent lighting and flicker on computer monitors.[2] 

Simulations of visual stress symptoms 

Myopia, which is measured in diopters by the strength or optical power of a corrective lens that focuses distant images on the retina, has also been classified by degree or severity:

  • Low myopia usually describes myopia of −3.00 diopters or less (i.e. closer to 0.00).
  • Medium myopia usually describes myopia between −3.00 and −6.00 diopters.Those with moderate amounts of myopia are more likely to have pigment dispersion syndrome or pigmentary glaucoma.
  • High myopia usually describes myopia of −6.00 or more.People with high myopia are more likely to have retinal detachments and primary open angle glaucoma.They are also more likely to experience floaters, shadow-like shapes which appear singly or in clusters in the field of vision. Roughly 30% of myopes have high myopia.

Age at onset
Myopia is sometimes classified by the age at onset:

Congenital myopia, also known as infantile myopia, is present at birth and persists through infancy.
Youth onset myopia occurs in the early childhood or teenage, and the ocular power can keep varying until the age of 21, before which any form of corrective surgery is usually not recommended by ophthalmic specialists around the world.
School myopia appears during childhood, particularly the school-age years.This form of myopia is attributed to the use of the eyes for close work during the school years.
Adult onset myopia
Early adult onset myopia occurs between ages 20 and 40.
Late adult onset myopia occurs after age 40 . [4]

There is significant evidence that many people inherit nearsightedness, or at least the tendency to develop nearsightedness. If one or both parents are nearsighted, there is an increased chance their children will be nearsighted.

   Even though the tendency to develop nearsightedness may be inherited, its actual development may be affected by how a person uses his or her eyes. Individuals who spend considerable time reading, working at a computer, or doing other intense close visual work may be more likely to develop nearsightedness.             eResearch by Navid Ajamin -- spring 2014

Nearsightedness may also occur due to environmental factors or other health problems:

  • Some people may experience blurred distance vision only at night. This “night myopia” may be due to the low level of light making it difficult for the eyes to focus properly or the increased pupil size during dark conditions, allowing more peripheral, unfocused light rays to enter the eye.
  • People who do an excessive amount of near vision work may experience a false or “pseudo” myopia. Their blurred distance vision is caused by over use of the eyes’ focusing mechanism. After long periods of near work, their eyes are unable to refocus to see clearly in the distance. The symptoms are usually temporary and clear distance vision may return after resting the eyes. However, over time constant visual stress may lead to a permanent reduction in distance vision.
  • Symptoms of nearsightedness may also be a sign of variations in blood sugar levels in persons with diabetes or an early indication of a developing cataract.[1]

  Actually, there are many possible factors, both known and unknown, which could account for such differences, and it would be very difficult to determine which factor is most important in any individual case. Some of these factors are:

  • The diet of the child
  • The diet of the mother during the gestation period
  • The distance the book is held from the eyes
  • The amount of light used for reading
  • How often the child looks up from the book
  • How large a "cushion" of farsightedness the child is born with
  • Hereditary factors [3]

See also:

Video:

Reference:

  1. aoa.org/patients-and-public/eye-and-vision-problems/glossary-of-eye-and-vision-conditions/myopia

  2. myopia.org/ebook/11chapter6.htm

 | 2014 © ^ نوشته شده توسط Navid Ajamin | 

Astigmatism (uh-STIG-muh-tiz-um) is a refractive error that prevents sufferers from seeing objects clearly from a distance or up close. Astigmatism may occur in varying degrees in each eye and can accompany myopia or hyperopia. Mild astigmatism is usually not noticeable, or causes only slight blurriness, while severe astigmatism causes objects to appear blurry at any distance. Approximately 80 percent of Americans have some degree of astigmatism, but many cases do not require correction.

Image of an Astigmatic Eye

A normal cornea is shaped like a perfect sphere. The eye’s natural lens is also curved in equal degree in all directions. The corneas or lenses of people with astigmatism do not have equal curves. One side may be steeper than the other, making the cornea look more like a football than a basketball. Because of this, light entering the eye is not focused correctly on the retina, resulting in a blurred image.[1]

Signs and symptoms of astigmatism may include

  • Blurred or distorted vision
  • Eyestrain
  • Headaches

When to see a doctor

If your quality of vision detracts from your enjoyment of activities or interferes with your ability to perform everyday tasks, see an eye doctor. An eye doctor can determine whether you have astigmatism, and if so, to what degree. He or she can then advise you of your options to correct your vision.

If you're a healthy adult older than 40, have your eyes examined about every two to four years until age 55. After age 55, have them checked every one to three years for signs of eye disease or problems, and then every one to two years after age 65. If you have eye problems, such as astigmatism, you may need to have your eyes checked more frequently. If you're at risk of certain eye diseases, such as glaucoma, or you have diabetes, check with your doctor to see how often you need to have your eyes examined.

Tests and diagnosis

To diagnose astigmatism, your eye doctor may:

        Measure reflected light. By measuring light reflected from the surface of your cornea, a device known as a keratometer quantifies the amount and orientation of corneal astigmatism.

        Measure the curvature of your cornea. Using light to project rings on to your cornea, a device called a keratoscope measures the amount of curvature to your cornea's surface and can confirm the presence of astigmatism. Observation through the keratoscope of the reflection of light from your cornea and inspection of the shape and spacing of the rings provide information about the degree of astigmatism.

To measure the change in corneal surface curvature, a process called corneal topography is used. Corneal topography uses a videokeratoscope, which is a keratoscope fitted with a video camera.[2] 

Levels of Astigmatism

Astigmatism is measured in units of diopters. In a prescription, plus and minus signs in the ‘cylinder’ box indicate the astigmatism prescription, which is then followed by numbers indicating the location (axis) of astigmatism. Here is a rough breakdown of the different degrees of astigmatism:

 

 0.25 to 0.75 diopters = mild astigmatism

1.00 to 2.50 diopters = moderate astigmatism

2.75 to 4.75 diopters = severe astigmatism
 
5.00 diopters or higher = extreme astigmatism

 To prescribe corrective wear for astigmatism, measurements are taken from a vertical and horizontal, or oblique approach, forming an axis. This is done because light enters the eye from different directions. Both the vertical and horizontal measurements will be different with astigmatism.
 

 

 

 

    

 Let’s use the letter T as an example. You have a vertical and horizontal part to the T. Light from each part of the T enters the eye at the same time. The vertical and horizontal parts of the T each have different prescriptions for the eye with astigmatism. Let’s say the vertical part of the T has a prescription of -3.00 while the horizontal part has a prescription of -5.00. Because the two prescriptions are 2.00 diopters or more apart, the person is considered to have severe astigmatism. In general, higher levels of astigmatism show a greater disparity between two prescriptions, and with milder astigmatism, the values are much closer to each other.

Astigmatism_text_blur 

The following are a few other abbreviations you may encounter on your eyeglass prescription:
  • SVD - Single Vision Distance, or glasses for distance only
  • SVN - Single Vision Near, or glasses for reading only 
  • Sphere - Spherical power has the same power in all meridians
  • Cylinder - A cylinder power corrects astigmatism and represents the difference in the greatest power of the eye and weakest power of the eye, usually separated by 90 degrees.
  • Axis - indicates the angle (in degrees) between the two meridians of an astigmatic eye
  • PD - (pupillary distance, or distance between the centers of the two pupils between the eyes) This measurement is essential to designing glasses that comfortable to wear and optically perfect. 
  • Prism - Prism is not commonly prescribed. It is often prescribed to displace the image in a certain direction for patients with crossed-eye (strabismus) or other eye muscle or focusing disorders.[3] 

 

 

 

Diagnosis 

  

 

Patients seek treatment because of blurred vision. A variety of tests can be used to detect astigmatism during the eye exam. The patient may be asked to describe the astigmatic dial, a series of lines that radiate outward from a center. People with astigmatism will see some of the lines more clearly than others.

Place yourself at approximately 1m from the screen

Cover one eye with your hand, without pressing on the lid, and take the test.

Cover the other eye and begin the test again. If some of the lines appear grayer and some blacker, you probably have an astigmatism - consult your eye care specialist. 

 

 

 One diagnostic instrument used is the keratometer. This measures the curvature of the central cornea. It measures the amount and direction of the curvature. A corneal topographer can measure a larger area of the cornea. It can measure the central area and mid-periphery of the cornea. A keratoscope projects a series of concentric light rings onto the cornea. Misshapen areas of the cornea are revealed by noting areas of the light pattern that do not appear concentric on the cornea.    eResearch by Navid Ajamin -- summer 2013

   

  Because these instruments are measuring the cornea, it is also important to have a refraction in case the lens is also contributing to the astigmatism. The refraction measures the optics or visual status of the eye and the result is the eyeglass prescription. The refraction is when the patient is looking at an eye chart and the doctor is putting different lenses in front of the patient's eyes and asks which one looks better.

Treatment

 Astigmatism can be treated by the use of cylindrical lenses. They can be in eyeglasses or contact lenses. The unit of measure describing the power of the lens system or lens is called the diopter (D). The lenses are shaped to counteract the shape of the sections of cornea that are causing the difficulty.

 

Because the correction is in one direction, it is written in terms of the axis the correction is in. On a prescription, for example, it may say 1.00 × 180°. Cylinders correct astigmatism, minus spheres correct myopia, and plus spheres correct hyperopia.

There is some debate as to whether people with very small amounts of astigmatism should be treated. Generally, if visual acuity is good and the patient experiences no overt symptoms, treatment is not necessary. When treating larger amounts of astigmatism, or astigmatism for the first time, the doctor may not totally correct the astigmatism. The cylindrical correction in the eyeglasses may make the floor appear to tilt, thus making it difficult for the patient at first.

astigmatism

Generally, the doctor will place lenses in a trial frame to allow the patient to try the prescription at the exam. It may take a week or so to get used to the glasses, however, if the patient is having a problem they should contact their doctor, who might want to recheck the prescription.[4]

Image: rugusavay.com alibaba.com eyecarekerry.com ej.iop.org brower.co.uk whatithinkabout.com onespecs.co.uk eyekit.co highburyeye.co.nz thewilltosee.com allaboutvision.com .cthospital.vn wrightoffer.com.my mediaspanonline.com la-sight.com vsp.com cxlusa.com luskeye.com optometrist.com.au fashioneyewear.co.uk eyeglassguide.ca toothwalker.org eylea.us crizal.com.sg

   

Reference: 1.eyehealthweb.com 2.mayoclinic.com  3.vision.about.com 4.encyclopedia.com


 | 2014 © ^ نوشته شده توسط Navid Ajamin | 

Convergence insufficiency occurs when your eyes don't turn inward properly while you're focusing on a nearby object. When you read or look at a close object, your eyes should converge — turn inward together to focus — so that they provide binocular vision and you see a single image. But if you have convergence insufficiency, you won't be able to move your eyes inward to focus normally.

 

Symptoms

 Not everyone with convergence insufficiency experiences symptoms. Signs and symptoms occur while you're reading or doing other close work and may include:

  • Tired, sore or uncomfortable eyes (eyestrain)
  • Headaches
  • Blurred vision
  • Difficulty reading — words seem to float on the page, you lose your place or you read slowly
  • Double vision
  • Difficulty concentrating
  • A "pulling" feeling around your eyes
  • Sleepiness
  • Squinting, rubbing or closing one eye

When to see a doctor

If you or your child experiences symptoms of convergence insufficiency or has problems reading, consult an eye care professional, such as an ophthalmologist or an optometrist. A technician called an orthoptist may assist the eye care professional in evaluating and treating convergence insufficiency.

Convergence insufficiency results from misalignment of the eyes when focusing on nearby objects. The exact cause isn't known, but the misalignment involves the muscles that move the eye. Typically, one eye drifts outward when you're focusing on a word or object at close range.

Complications

Difficulties with reading and concentrating can adversely affect a child's learning. Convergence insufficiency typically isn't detected in routine eye exams or school-based vision screenings. A child with the condition may be evaluated for learning disabilities because of his or her reading troubles.

 

Tests and diagnosis

People with convergence insufficiency may have otherwise normal or "20-20" vision, and the condition may not be detected during a routine eye exam. To diagnose convergence insufficiency, your eye doctor may do the following, including special eye-focusing tests:

  • Take a medical history. This may include questions about problems you have with focusing, blurred or double vision, headaches, and other signs and symptoms.
  • Measure the near point of convergence (NPC). This test measures the distance from your eyes to where both eyes can focus without double vision. For this simple test, the examiner holds a small target, such as a glass ball, printed card or penlight, in front of you and slowly moves it closer to you until either you experience double vision or the examiner recognizes that your eyes can no longer focus together.
  • Assess positive fusional vergence (PFV). During this test, you're asked to read letters on an eye chart while looking through prism lenses. The examiner will note when you begin to have double vision.
  • Perform a routine eye exam. If you have any other vision problems, such as nearsightedness, your ophthalmologist or optometrist may conduct tests to assess the degree of the problem.

Treatments and drugs

If convergence insufficiency isn't causing symptoms, you generally don't need treatment. But for people with symptoms, treatment with eye-focusing exercises can increase the eyes' convergence ability. Treatment may take place in the office of a trained therapist or at your home.

 Treatments may include:

 

  • Pencil pushups. In this simple exercise, you focus on a small letter on the side of a pencil as you move it closer to the bridge of your nose, stopping the movement if you have double vision. The exercise is often done for 15 minutes a day, five or more days a week.

 

  • Computer vision therapy. Eye-focusing exercises are done on a computer using special software designed to improve convergence. You may print out the results to share with your eye doctor.
  • Reading glasses. Glasses with built-in prisms force your eyes to work harder to align and are sometimes used for people who need help with their reading vision. But they can be tiring to your eyes and generally haven't proved effective.

 

             A study sponsored by the National Eye Institute of the National Institutes of Health compared home-based treatment with doctor office-based treatment for convergence insufficiency in children ages 9 to 17. Study results showed that the most effective therapy was a weekly hourlong session of in-office vision therapy with at-home reinforcement exercises. Other studies have also found that office-based treatment is effective about 75 percent of the time.

Home-based treatment with pencil pushups or computer programs hasn't been shown to be as effective — in some studies, it works only about one-third of the time. But home treatment costs less and is more convenient. Only a small percentage of eye care providers offer in-office therapy for convergence insufficiency. Many people who can't find or can't afford in-office therapy opt for home-based treatment.

If you choose home treatment, many experts recommend using computer software programs along with pencil pushups. The combined approach may be more effective, and the computer therapy is more engaging for children.

Treatment for convergence insufficiency may take three months or longer, though you'll likely start to see improvement in your symptoms after four weeks. After your convergence ability has improved, you can help maintain your improved vision by continuing to read and do other near tasks. Treatment can permanently cure convergence insufficiency, but symptoms may come back after an illness, lack of sleep or when you're doing a lot of reading or other close work. In rare cases, eye-focusing exercises don't work and your doctor may recommend surgery.

eResearch by Navid Ajamin -- spring 2013

See Also: What is Convergence Insufficiency?      Research on Vision Therapy

Image: fvdcpc.com improveeyesighthq.com advancedeyehospital.com

Reference: mayoclinic.com


 | 2014 © ^ نوشته شده توسط Navid Ajamin | 

Can you see clearly now? Probably not — changes in your vision during pregnancy often stick around until after you deliver.

What blurred vision during pregnancy is

Difficulty with your vision and dry, irritated eyes are common pregnancy symptoms.
 

What causes blurred vision pregnancy

Pregnancy hormones (what else?) that decrease tear production (ironically, since they certainly don't decrease crying!), leading to eye dryness, irritation, and discomfort. Hormones also cause fluid buildup in your eyes, the same way they make you have swollen ankles and feet. This can lead to changes in the curvature of your eye, which causes a change in your vision during pregnancy.

 

What you need to know about blurred vision pregnancy

Changes in vision are normal for many women during pregnancy. You might not see as well, or your contact lenses might feel less comfortable. Luckily, these changes are temporary and your vision should go back to normal after delivery. Remember, however, that some serious vision problems can be a sign of gestational diabetes or high blood pressure, so be sure to mention any vision changes to your practitioner.

 

 

What to do about blurred vision pregnancy

  • If you wear glasses or contacts, don't bother with a new prescription until after you've had your baby.
  • If your contacts are bothering you, consider wearing your glasses until after delivery, or use lubricating drops recommended by your eye doctor if your eyes feel especially dry. (You can use drops even if you don't wear contacts.)
  • Steer clear of corrective eye surgery six months before conceiving, during pregnancy, and for six months after delivery, according to ophthalmologists. It won't hurt your baby, but it might lead to over-correction, which could require another surgery later on.   eResearch by Navid Ajamin -- spring 2013

If you notice blurring, dimming vision, spots, and floaters that don't go away, or double vision that persists for more than two hours, call your practitioner.

Reference: www.whattoexpect.com                       

 

See Also:

Causes of blurred vision

Blurred Vision During Pregnancy Causes & Symptoms


 | 2014 © ^ نوشته شده توسط Navid Ajamin | 

نام دیگر دو بینی دیپلوپیا است که در آن از یک شی دو تصویر دیده می شود.

 

به طور کلی دو نوع دوبینی وجود دارد: الف)دوبینی تک چشمی ب)دوبینی دوچشمی

زمانی که یک بیمار با نا رضایتی از دوبینی مراجعه می کند ابتدا باید مشخص شود:

 1- در کجا دو تصویر از هم فاصله گرفته اند و در کجا در هم رفته اند.

 2- آیا به صورت افقی یا عمودی از هم جداشده اند. اگرچه بیشتر شکایات دوبینی درنتیجه مشکلات دید دوچشمی است، اما از دلایل احتمالی دیگراین مشکل می توان به عیب انکساری اصلاح نشده و دوبینی تک چشمی اشاره نمود. درعیب انکسار اصلاح نشده ممکن است بیمار بیان کند که دو تصویر به طور کامل از هم جدا نیستند و تمایل به ادغام شدن دارند. ممکن است در این حالت شکایت بیمار به دلیل آستیگمات اصلاح نشده یا حتی دوبینی اصلاح نشده ای باشد که با تطابق اصلاح نمی شود و یا ممکن است پیر چشمی باشد.

  • دوبینی تک چشمی(monoculal diplopia) :

به دوبینی گویند که تنها در یک چشم وجود دارد. این دوبینی حتی زمانی که چشم دیگر بسته است ادامه می یابد و زمانی که فرد به جهت دیگری نگاه می کند هم این دوبینی از بین نمی رود.اگر حدس زده شود که دلیل شکایت بیمار از دوبینی، دوبینی تک چشمی باشد باید از بیمار سوال شود که آیا وقتی یک چشم بسته است این اتفاق می افتد؟ دلایل کلاسیک برای دوبینی تک چشمی قوز قرنیه است. بیمار با کراتوکونوس علاوه بر دوبینی تک چشمی از آزار و ضعف بینایی در حین استفاده از عینک شکایت دارد. از علائم کلینیکی قوز قرنیه می توان به موارد زیر اشاره نمود:

نازک بودن و برجستگی راس قرنیه که با اسلیت لمپ مشاهده می شود و انحنای زیادی که در کراتومتری دیده می شود و در رتینوسکوپی رفله نور به صورت موج دار است.زمانی که بیمار به پایین نگاه می کند برجستگی های قرنیه ممکن است به صورت دندانهای در پلک پایین دیده شود. دوبینی تک چشمی می تواند در اثر عوامل زیر ایجاد شود:

1- استیگماتیسم

2- کراتوکونوس (قوز قرنیه)

3- ناخنک (pterygium): ضخیم شدگی در ملتحمه، لایه موکوسی که سطح داخلی پلکها و قسمت سفید چشم را می پوشاند. این ضخیم شدگی به سمت قرنیه افزایش می یابد.

4- کاتاراکت: شفافیت لنز به مقدار زیادی کاهش می یابد. از جمله ریسک فاکتورهای آن می توان به موارد زیر اشاره کرد:

سن بالای 65 سال، تروما یا ضربه به چشم، دیابت طولانی مدت، سیگار کشیدن، استفاده از داروهای استروئیدی و یا استفاده از درمانهای رادیولوژی

5- جابه جایی لنز: لیگامان یا رباطی که به لنز متصل است و آنرا نگه می دارد، پاره می شود و لنز جابه جا می گردد.دلیل این اتفاق می تواند ترومای چشم و یا حالتی باشد که سندروم مارفان نامیده می شود.

6- خشکی چشم

7- بعضی از مشکلات رتین: زمانی که سطح رتین کاملا صاف نباشد (که دلایل مختلفی دارد) ممکن است دوبینی تک چشمی ایجاد گردد.

8- چند مردمکی بودن

  •  دو بینی دوچشمی (binocular diplopia)

که در آن چشم ها راستای خود را از دست می دهند. این دوبینی زمانی که یک چشم بسته میشود متوقف می شود. ماهیچه های اطراف کره چشم جهات نگاه را تنظیم می کنند و هر مشکلی که این ماهیچه ها را تحت تاثیر قرار دهد می تواند موجب دو بینی شود. از جمله:

I. استرابیسم: به مشکلی گویند که در دوران کودکی چشم ها راستای خود را از دست می دهند و حدود %4 از کودکان زیر 6 سال را تحت تاثیر قرار می دهد.

II. آسیب به اعصاب کنترل کننده ماهیچه های خارج چشمی: اعصاب به دلیل آسیب های مغزی آسیب می بینند. دلایل آسیب های مغزی: عفونت، اسکلروزیس چندگانه؟؟؟، سکته مغزی، ترومای سر یا تومور مغزی به ویژه توموری که در انتهای تحتانی مغز واقع شده باشد.، تومور یا ترومایی که به سمت حدقه چشم رشد می کند می تواند در طول مسیر عصب به عضله چشمی به هر قسمت از عصب آسیب وارد کند.

III. دیابت: این بیماری می تواند موجب آسیب به یکی یا تعداد بیشتری از اعصاب کنترل کننده حرکات چشم شود. حتی در بسیاری از موارد قبل از آنکه فرد متوجه دیابت خود شود، این اتفاق می افتد. میاستنی گراویس که نوعی بیماری عصب- عضله ای است باعث می شود که عضله به راحتی خسته شده و در نهایت ضعیف شود. دلیل این بیماری: سیستم ایمنی اشتباها مکانهایی را که عصب ایمپالسهایی را به عضله منتقل می کند و موجب انقباض عضله می گردد را مورد حمله قرار می دهد.

IV. بیماری های گراوز: این بیماری عمومی ترین اثر پرکاری تیروئید است و در بعضی از افراد با بیماری گراوز دو بینی نیز پیشرفت می کند که این می تواند به این علت باشد که ماهیچه های کنترل کننده حرکات چشم در داخل حدقه موج دار و یا کلفت می شوند.

V. ترومای ماهیچه های چشمی: ماهیچه های حدقه چشم ممکن است به دلیل ضربه به صورت به ویژه به دلیل شکستگی استخوانهای نازک چشم آسیب ببینند.

 Diagnosis

اولین قدم این است که بفهمیم آیا دوبینی تک چشمی است یا دو چشمی! برای این کار ابتدا از بیمار می خواهیم یک چشم خود را بپوشاند و پس از آن نوبت به چشم دیگر است که باید آن را بپوشاند. اگر بیمار دوبینی تک چشمی داشته باشد باید مواردی مثل کاتاراکت و ... را در مورد او بررسی نمود. اگر دوبینی دوچشمی باشد و هیچ تروما یا ضربه ای صورت نگرفته باشد، باید بیمار از لحاظ ابتلا به دیابت ، بیماری های گراوز و یا اختلالات عصبی بررسی شود. در تشخیص دوبینی دوچشمی باید بفهمیم کدام ماهیچه چشمی تحت تاثیر قرار گرفته است. برای دانستن این مساله باید از بیمار بخواهیم به تارگتی که به جهات بالا، پایین، چپ و راست حرکت داده می شود نگاه کند. این تست این امکان را به ما می دهد تا بفهمیم هر چشم در هر جهت چه اندازه حرکت می کند. بعد از آن از بیمار می خواهیم بر روی یک تارگت فوکوس کند وبه نوبت چشم هایش را می بندیم.(cover test)  اگر مشاهده کردیم که چشم های بیمار در حین جابه جا کردن کاور جابه جا می شوند، این بدین معناست که چشم ها با هم کاملا هماهنگ نیستند. ممکن است برای جابه جا نمودن تصویر و تکرار تست، پریزم هایی را مقابل چشم بیمار قرار دهیم. این کار امکان تشخیص واندازه گیری درجه یا مقدار دوبینی را زمانی که بیمار به جهات مختلف نگاه می کند را به ما می دهد .برای تشخیص اینکه آیا فرد نیاز به انجام تست های بیشتر دارد یا نه، باید نتیجه تست ها را به همراه یک تاریخچه کامل از بیماری های چشمی فرد و دیگر علائم اضافی که در تشخیص به ما کمک می کنند را مورد بررسی قرار دهیم. به طور مثال: اگر حدس زدیم که بیمار پرکاری تیروئید دارد بیمار باید آزمایش خون بدهد تا سطح هورمون های تیروئیدی وی مشخص گردد. اگر حدس زدیم که به دلایلی اعصاب ماهیچه های چشمی بیمار در گیر شده، بیمار نیاز به یک MRI و یا CTاسکن از ناحیه سر خود دارد، تا از نظر تروما، خونریزی، تومور یا نقص رگهای خونی در مغز بررسی شود.

اغلب اوقات پی بردن به دوبینی در بزرگسالان ساده است، چون آنها می توانند آنچه را که می بینند توصیف کنند. تشخیص در کودکان سخت تر است چون نمی توانند توصیف خوبی از دیده های خود ارائه دهند. والدین این کودکان ممکن است متوجه شده باشند که کودکشان لوچ است، یا چشمش را با یک دستش می پوشاند، سر خود را به صورت غیر نرمال کج می کند و یا از پهلو نگاه می کند.

مشکلات دید دوچشمی:

اگر دوبینی تنها گاهی اوقات اتفاق بیفتد، ممکن است بینار متوجه شود که برای فواصل دور یا نزدیک و یا هر دو مقدار انحراف دارد؛ به طور مثال بیماری که انحراف زیادی دارد ممکن است برای انجام اعمال و وظایفش در فواصل دور(مثل رانندگی) دوبینی گهگاهی را تجربه کرده باشد. یا بیماری که دچار نقص در سیستم تقارب خود است ممکن است از دوبینی به دنبال کار نزدیک طولانی مدت شکایت کند. اگر فرد دوبینی گهگاهی عمدی را تجربه کند، ممکن است دلیل آن فوریا عمودی همرا با فیوژن عمودی ناکافی باشد.

بیماران با سابقه استرابیسم به ندرت از دوبینی شکایت دارند، چون قبلا از طریق ساپرس کردن، فیکسیشن خارج از مرکز،آمبیلوپی و یا مجموعه ای از این ها، با این وضعیت سازگاری پیدا کرده اند.به هر حال اگر دوبینی اخیرا شروع شده باشد احتمال فلج شدن ماهیچه وجود دارد. در بیماران مسن باید توجه ویژه ای به احتمالات اجزاء عمودی دوبینی کرد: احتمالا علت دو بینی پارگی رگهای مغزی مثل پاره شدن حلقه ولیس باشد.

دوبینی متقاطع و غیر متقاطع:

معمولا افرادی که به طرفین انحراف دارند (Lateral phoria) زمانی که چشم ها از هم جدا می شوند ممکن است دوبینی متقاطع یا غیر متقاطع را تجربه کنند. برای درک مفهوم دوبینی متقاطع از غیر متقاطع لازم است رابطه ی بین میدان بینایی و تصویر رتینال را بشناسیم؛ که این رابطه عبارت است از: تصویر اشیاء موجود در سمت راست میدان بینایی، سمت چپ رتین و تصویر اشیاء سمت چپ میدان بینایی سمت راست رتین تشکیل می شود.

در افرادی که اگزوفوریا دارند تصویر جسمی که باید بر روی فووا دو چشم تشکیل شود، مثلا در چشم راست آنها این تصویر، سمت راست فووا تشکیل می شود و فرد تصور می کند که شیء در سمت چپ میدان بینایی اش قرار دارد؛ یعنی فرد دو تصویر می بیند. تصویری که توسط چشم راست دریافت می شود سمت چپ تصویر چشم چپ دیده می شود. در نتیجه دوبینی که رخ می دهد از نوع متقاطع است.

در بیمارانی که ایزوفوریا دارند تصویر شیء مورد نظر سمت چپ فووا چشم راست تشکیل می شود؛ پس تصویری که توسط چشم راست درک می شود سمت راست تصویری است که توسط چشم چپ درک می شود. در نتیجه دوبینی غیر متقاطع بوجود می آید.

 

 

مدت زمان مورد انتظار (Expected duration)

 این که چه مدت دوبینی ادامه می یابد بستگی به علت ایجاد کننده آن دارد. به طور مثال کاتاراکت و ناخنک ممکن است در طول زمان بدتر شوند؛ ولی هر دو می توانند از طریق عمل جراحی تصحیح شوند. در فردی که دوبینی وی به علت دیابت است، اعصاب اغلب بعد از چند ماه دوباره رشد می کنند. زمانی که این دو اتفاق می افتد دوبینی تقریبا ناپدید می شود. بچه هایی که به دلیل استرابیسم دچار دوبینی شده اند، با درمان استرابیسم، دوبینی آنها بهبود می یابد.

پیشگیری (prevention)

بعضی از موارد دوبینی قابل پیشگیری هستند. برای کمک به پیشگیری از دوبینی ناشی از ترومای سر در هنگام رانندگی باید از کمربند ایمنی استفاده نمود؛ در طول فعالیتهای ورزشی و کارهایی که احتمال آسیب چشمی در آنها زیاد است از عینک و کلاه ایمنی استفاده شود؛افراد دیابتی می توانند با کنترل قند خون خود احتمال آسیب عصبی که موجب دوبینی می شود را کاهش دهند. برای جلوگیری دوبینی ناشی از کاتاراکت و سایر عوامل راهی وجود ندارد.

درمان (Treatment)

درمان دوبینی بستگی به دلایل ایجاد کننده آن دارد. برای مثال در افرادی که آستیگمات باعث دوبینی آنها شده می توان از کنتاکت لنزهای ویژه استفاده نمود. گاهی اوقات به راحتی می توان با به روز کردن عینک تجویز شده از بروز مشکلات جلوگیری کرد. برای درمان کاتاراکت و ناخنک از جراحی استفاده می شود. همچنین جراحی بر روی ماهیچه ها نوع خاصی از دوبینی را درمان می کند. اغلب در این جراحی ها از بخیه هایی قابل تنظیم استفاده می شود که وضعیت چشم ها چند ساعت پس از جراحی هماهنگ شود. همچنین می توان با به کار بردن منشور در عینک تجویزی، تصویری که توسط یک چشم ایجاد می شود با تصویر چشم دیگر را هماهنگ کردن و منطبق کردن کرد. برای کودکانی که استرابیسم دارند درمان شامل: پوشاندن عینک تجویز شده، پریزم درمانی برای مرتب کردن چشم ها در یک ردیف، ویا جراحی است.دوبینی ایجاد شده بر اثر داروهای شیمیایی یا عصبی ممکن است یا درمان ان بیماری بهبود یابد. تزریق بوتولینم می تواند ماهیچه های قوی تر را تضعیف کند تا با هماهنگ شدن با ماهیچه های ضعیفتر یک بالانس بینایی ایجاد شود.اولین تستی که از بچه ها گرفته می شود باید قبل از 6 ماهگی و همراه با تست های follow up در سنین 3 سالگی باشد. افراد مسن تر از 40 سال حتی اگر مشکل بینایی قابل توجهی هم نداشته باشند، باید هر دو سال یک بار چک شوند.

تست میدان دوبینی

در تست broad H ، اگر چشمی در هر یک از حرکات میدان، نسبت به چشم دیگر تاخیر داشته باشد، از بیمار می خواهیم یک جفت عینک RED-GREEN بزند (لنز قرمز روی چشم راست!). در حالی که تست broad H (H پهن و عریض) تکرار می شود از بیمار می خواهیم گزارش کند که آیا 2 نور (یکی قرمز و دیگری سبز) در دو میدان دید با نگاه ثابت و خیره دیده می شوند یا نه؟! و اگر چنین است چه میزان فاصله بین دو تا نور وجود دارد. فرض می کنیم که بیمار گزارش کرد دوبنی در قسمت تحتانی سمت چپ میدان دید وی وجود دارد و نور سبز نسبت به نور قرمز در سمت پریفرال تری قرار می گیرد. ماهیچه مستقیم با همان نام برای سمت چپ تحتانی میدان، L.I.R (Left Inferior Rectus) نام دارد. در حالی که ماهیچه مایل با نام مخالف برای آن قسمت میدان R.S.O (Right Superior Oblique) می باشد.چون بیشترین تصویر پریفرال مربوط به چشم چپ (تصویر سبز رنگ) می شود، L.I.R ماهیچه معیوب می باشد. [1]    eResearch by Navid Ajamin -- autumn 2012

BINOCULAR DIPLOPIA


Double vision can occur when the two eyes are not correctly aligned while aiming at an object, such as in esotropia and exotropia - these result in uncrossed diplopia and crossed diplopia, respectively (i.e. "crossed eyes", in esotropia, result in uncrossed diplopia). When the eyes are misaligned and aimed at different targets, two non-matching images are sent to the viewer's brain. When the viewer's brain accepts and uses two non-matching images simultaneously, double vision results.

Double vision is dangerous to survival, therefore, the brain naturally guards against its occurrence. In an attempt to avoid double vision, the brain can ignore one eye (suppression). Due to the brain's ability to suppress one eye, double vision can appear to go away without medical evaluation or treatment. The causes of the double vision are very likely still present and loss of vision in one eye can occur due to lack of treatment. The loss of vision in one eye can be temporary or permanent depending on detection and treatment. It is in this way, that diplopia contributes to loss of depth perception and binocular vision, amblyopia (lazy eye), and/or strabismus (deviating eye).

MONOCULAR DIPLOPIA

Diplopia can also occur when viewing with only one eye; this is called monocular diplopia, or where the patient perceives more than two images, monocular polyopia. In this case, the multiple vision can be caused by a structural defect in the vision system, such as cataracts, subluxation of the crystalline lens or Keratoconus causing irregularities in the refraction of light within the eye.

TEMPORARY DIPLOPIA
Temporary diplopia can also be caused by intoxication from alcohol or head injuries, such as concussion. If temporary double vision does not resolve quickly, one should see an eye doctor immediately. It can also be a side effect of the anti-epileptic drugs Phenytoin and Zonisamide.[2]

Causes

 

Diplopia has a diverse range of ophthalmologic, infectious, autoimmune, neurological, and neoplastic causes.

  • Damage to the third, fourth, or sixth cranial nerves, which control eye movements.
  • Cancer
  • Trauma
  • Diabetes
  • Migraine
  • Multiple sclerosis
  • Fluoroquinolone antibiotics
  • Botulism
  • Guillain-Barré syndrome
  • Brain tumor
  • Sinusitis
  • Abscess
  • Wernicke's syndrome
  • Graves disease
  • Drunkenness
  • Orbital myositis
  • Myasthenia gravis
  • Anisometropia
  • Salicylism
  • Strabismus
  • Lyme Disease
  • .... [3]

 Reference:

See Also:


 | 2014 © ^ نوشته شده توسط Navid Ajamin | 

ديابت مي­تواند روي ديد تاثير بگذارد

در صورتيكه شما به بيماري ديابت مبتلا هستيد بدن شما نمي­تواند بدرستي از قند استفاده و آنرا ذخيره كند. ديابت باعث افزايش قند خون، عطش بيش از حد و تكرر ادرار و همچنين تغييراتي در رگهاي خوني بدن ( سرخرگها و سياهرگها) مي­شود. ديابت مي­تواند به اشكال مختلف روي ديد تاثير بگذارد. باعث ايجاد آب مرواريد ، آب سياه و مهمتر از همه صدمه به رگهاي خوني داخل چشم مي­شود.

رتينوپاتي ديابتي چيست؟

رتينوپاتي ديابتي عارضه اي ناشي از ديابت است كه بدليل تغييرات ايجاد شده در رگ هاي خوني رخ مي دهد. پرده شبكيه لايه عصبي در پشت چشم است كه نور را درك مي­كند و تصاوير را به مغز مي­فرستد. وقتي عروق خوني در شبكيه آسيب مي­بينند ممكن است باعث نشت مايع يا خون شده يا منجر به رشد شاخه­هاي عروقي شكننده و كلافه مانند شده و باعث تخريب شبكيه شود در نتيجه تصويري كه شبكيه به مغز مي­فرستد تار شده يا كج و معوج مي­شود.

رتينوپاتي ديابتي يكي از علل اصلي كاهش ديد است و كسانيكه ديابت درمان نشده دارند 25 برابر شانس بيشتري براي كوري نسبت به افراد عادي دارند.

هرچه طول بيماري ديابت بيشتر باشد احتمال رتينوپاتي ديابتي بيشتر مي­شود. در نزديك به 80% كسانيكه لااقل 15 سال ديابت دارند مقداري صدمه به عروق شبكيه ديده مي­شود. در مبتلايان به ديابت نوع يك (نوع جوانان ) احتمال ابتلا به رتينوپاتي ديابتي در سنين پايين تر بيشتر است. چنانچه شما ديابت داريد بايستي بدانيد كه امروزه با بهبود وسائل تشخيصي و درماني، فقط درصد كوچكي از بيماران مبتلا به ديابت مشكلات جدي ناشي از كاهش ديد خواهند داشت، مشروط به اينكه به موقع به چشم پزشك مراجعه نمايند.

انواع رتينوپاتي

 

Diabetes Type

Duration of Disease

Probability of Retinopathy

Probability of Progression

Type I

10 years

60 to 74%

Unspecified

Type I

15 years

98%

25% proliferative retinopathy

Type I

20 years

100%

50% proliferative retinopathy

Type II

At diagnosis

10 to 20%

Unspecified

Type II

4 years

4 to 29%

Unspecified

Type II

15 years

60 to 80%

5 to 20% proliferative retinopathy

Table1. Incidence of retinopathy relative to duration of Type I and Type II diabetes http://lieyecare.com/diabetic.html

رتينوپاتي زمينه اي مرحله اول رتينو پاتي ديابتي است. در اين مرحله عروق كوچك در پرده شبكيه صدمه ديدهو مايع يا خون از آنها نشت مي­كند. مايع نشت كرده باعث تورم پرده شبكيه شده و يا رسوباتي بنام "اگزودا" را ايجاد مي­نمايد.

با اينكه اين مرحله معمولاً روي ديد تاثيري نمي­گذارد اما ممكن است بعداً به مراحل شديدتري كه منجر به كاهش ديد مي­شود تبديل شود. از اين رو رتينوپاتي زمينه اي به عنوان يك علامت هشداردهنده محسوب مي­شود.

گاهي مايعي كه نشت كرده است در مركز ديد جمع مي­شود. مركز ديد مسئول ديدن جزئيات ريز اشيا مي­باشد (مثلاً حروف يا اعداد). اين مسئله بنام تورم مركز ديد خوانده مي­شود و ممكن است سبب شود خواندن يا انجام كارهاي نزديك مشكل­تر شود.

رتينوپاتي پروليفراتيو(تكثيري) حالتي است كه رگهاي خوني جديد و غيرطبيعي بروي سطح شبكيه رشد مي­كنند. اين پديده "نئوواسكولاريزاسيون - Neovascularization" خوانده مي شود. اين عروق جديد ديواره ضعيف­تري داشته و شكننده هستند و ممكن است منجر به خونريزي شوند. زجاجيه ماده شفاف و ژله مانندي است كه مركز چشم را پر مي­كند. خون نشت كرده باعث كدر شدن زجاجيه شده و بصورت نسبي عبور نور را از مردمك به پرده شبكيه را مانع مي­شود در نتيجه تصوير تار و درهم مي­شود . اين رگهاي خوني غيرطبيعي ممكن است تبديل به بافت سفتي شده كه شبكيه را از پشت چشم جدا كنند و باعث جدا شدگي پرده شبكيه شوند كه در صورت عدم درمان مي­تواند منجر به كاهش شديد ديد و كوري شود.

رگهاي خوني غيرطبيعي همچنين ممكن است اطراف مردمك ، روي عنبيه (قسمت رنگي چشم) رشد كرده و با افزايش فشار داخل چشم باعث ايجاد آب سياه شود.

رتينوپاتي ديابتي تكثيري (پروليفراتيو) شديدترين نوع بيماري شبكيه ناشي از ديابت مي­باشد. حدود 20% افراد ديابتي به آن مبتلا مي­شوند و مي­تواند باعث كاهش شديد ديد و كوري شود.

علائم رتينوپاتي ديابتي كدامند؟

معمولاً در مرحله رتينوپاتي زمينه اي علامتي وجود ندارد. اگرچه ممكن است در صورت ايجاد تورم مركز ديد تاري ديد بصورت تدريجي ايجاد شود. شما ممكن است هرگز به تغيير ميزان ديد خود پي نبريد. معاينه چشم پزشكي تنها راهيست كه به كمك آن مي­توان تغييرات داخل چشم شما را پيدا كرد.

وقتيكه خونريزي ايجاد مي­شود ديد شما تار شده، لكه­هايي در آن پيدا مي­شود و حتي ممكن است بكلي ديد شما از بين برود. رتينوپاتي ديابتي پروليفراتيو اگرچه بدون درد است اما شكل شديدي از بيماري است و نيازمند توجه پزشكي فوري است. حاملگي و افزايش فشار خون ممكن است رتينوپاتي ديابتي را تشديد كنند.


چگونه رتينوپاتي ديابتي تشخيص داده مي­شود؟

بهترين راه براي تشخيص رتينوپاتي ديابتي معاينه چشمي در فواصل منظم مي­باشد كه توسط چشم پزشك بايستي انجام شود. رتينوپاتي بسيار شديد ممكن است كاملاً بدون علامت باشد. بيماري را مي­توان با درمان بهبود بخشيد. براي تشخيص رتينوپاتي ديابتي چشم پزشك با استفاده از دستگاهي بنام افتالموسكوپ بداخل چشم شما نگاه مي­كند. چشم پزشكي ممكن است قبل از معاينه با استفاده از قطره چشمي مردمك را باز كند.

چنانچه چشم پزشك رتينوپاتي ديابتي را تشخيص دهد ممكن است نياز به عكس رنگي ته چشم يا آزمايش خاصي بنام "آنژيوگرافي با فلوئورسئين" باشد تا مشخص شود كه شما احتياج به درمان داريد يا نه؟ در آنژيوگرافي با فلوئورسئين يك ماده رنگي به داخل رگ شما تزريق مي­شود و عكسهاي مخصوصي از چشم شما گرفته مي­شود.

چگونه رتينوپاتي ديابتي درمان مي­شود؟

براي درمان چشم پزشك مسائل زير را در نظر مي­گيرد:

  • سن شما
  • تاريخچه پزشكي شما
  • چگونگي نحوه زندگي شما
  • چه مقدار شبكيه صدمه ديده است ؟

در بسياري موارد احتياجي به درمان نيست اما بيمار بايد بطور مرتب تحت معاينات چشمي قرار گيرد. در ديگر موارد، درمان براي متوقف كردن صدمات ناشي از رتينوپاتي ديابتي و در صورت امكان بهبود ديد انجام مي­شود.

كرايوتراپي(سرد كردن): اگر زجاجيه بدليل وجود خون كدر باشد جراحي ليزر را تا زمانيكه خون جذب شود نميتوان انجام داد. در بعضي موارد خونريزي زجاجيه، كرايوتراپي يا يخ زدن شبكيه ممكن است در كوچك شدن رگهاي خوني غيرطبيعي كمك كننده باشد.

ويتركتيومي (برداشتن زجاجيه): در رتينوپاتي ديابتي پروليفراتيو پيشرفته ممكن است چشم پزشك برداشتن زجاجيه را توصيه كند. اين جراحي ميكروسكوپي در اطاق عمل انجام مي­شود. ويتركتيومي زجاجيه پر شده از خون را بر مي دارد و به جاي آن ماده شفافي را جايگزين مي­كند. در حدود 70% بيماران بعد از برداشتن زجاجيه بهبودي ديد دارند . گاهي اوقات قبل از انجام عمل برداشتن زجاجيه چشم پزشك ممكن است براي چند ماه يا يكسال صبر كند تا شايد خونريزي خود بخود جذب شود.

ترميم شبكيه: در صورتيكه بافت تخريب شده منجر به جداشدگي شبكيه از پشت چشم شود كاهش شديد ديد يا كوري را باعث مي­شود مگر اينكه جراحي براي چسباندن شبكيه بموقع و با موفقيت انجام شود.

نقش بيمار در درمان چيست ؟

مراقبت موفقيت آميز رتينوپاتي ديابتي فقط به درمان اوليه توسط چشم پزشك شما بستگي ندارد. طرز برخورد و توجه شما به درمان داروئي و رعايت رژيم ديابتي ضروري است. شما بايستي ميزان مناسب قند خون خود را حفظ كنيد. از سيگار كشيدن خودداري كنيد و به فشار خون خود نيز توجه داشته باشيد. فعاليتهاي فيزيكي معمولاً براي بيماران مبتلا به رتينوپاتي ديابتي مسئله اي نيست . گاهي در بيماران مبتلا به نوع فعال رتينوپاتي پروليفراتيو محدود كردن فعاليتهاي فيزيكي توصيه مي­شود.

كاهش ديد به ميزان زيادي قابل پيشگيري است

  • رتينوپاتي ديابتي ممكن است بدون هيچ گونه علامتي وجود داشته باشد.
  • تشخيص اوليه رتينوپاتي ديابتي بهترين روش براي جلوگيري از كاهش ديد است.
  • بيماران مبتلا به ديابت بايستي حداقل سالي يكبار توسط چشم پزشك معاينه شوند. وقتيكه رتينوپاتي ديابتي ايجاد شد معاينات بيشتر چشم پزشكي با فواصل كمتر ضروري است.
  • با كنترل دقيق چشم پزشك مي­توانيد درمان را قبل از صدمه ديد شروع كنيد.

      eResearch by Navid Ajamin -- summer 2012

Image: greathabitsgreatvision.com ; lieyecare.com ; eyeweekly.cteyecaregroup.com ; blogs.nejm.org ; wikimedia.org

Reference: farmaniehospital.com ; www.iran.pezeshk.us  روزنامه پزشکی ایران

See Also: diabetic retinopathy ; رتینوپاتی دیابتی


 | 2014 © ^ نوشته شده توسط Navid Ajamin | 

The optic nerve contains axons of nerve cells that emerge from the retina, leave the eye at the optic disc, and go to the visual cortex where input from the eye is processed into vision. There are 1.2 million optic nerve fibers that derive from the retinal ganglion cells of the inner retina.

 Optic neuropathy refers to damage to the optic nerve due to any cause. Damage and death of these nerve cells, or neurons, leads to characteristic features of optic neuropathy. The main symptom is loss of vision, with colors appearing subtly washed out in the affected eye. On medical examination, the optic nerve head can be visualised by an ophthalmoscope. A pale disc is characteristic of long-standing optic neuropathy. In many cases, only one eye is affected and patients may not be aware of the loss of color vision until the doctor asks them to cover the healthy eye.

 

Optic neuropathy is often called optic atrophy, to describe the loss of some or most of the fibers of the optic nerve. In medicine, "atrophy" usually means "shrunken but capable of regrowth", so some argue that "optic atrophy" as a pathological term is somewhat misleading, and the term "optic neuropathy" should be used instead.

In short, optic atrophy is the end result of any disease that damages nerve cells any where between the retinal ganglion cells to the lateral geniculate body(anterior visual system).

Optic NeuritiseResearch by Navid Ajamin -- summer 2012

Reference: Optic neuropathy From Wikipedia, the free encyclopedia

See Also: Optic nerve atrophy U.S. National Library of Medicine


 | 2014 © ^ نوشته شده توسط Navid Ajamin | 

Age-related macular degeneration (AMD) is a medical condition which usually affects older adults and results in a loss of vision in the center of the visual field (the macula) because of damage to the retina. It occurs in “dry” and “wet” forms. It is a major cause of blindness and visual impairment in older adults (>50 years). Macular degeneration can make it difficult or impossible to read or recognize faces, although enough peripheral vision remains to allow other activities of daily life.[1]

Macular Degeneration - Symptoms and Detection
Symptoms of Dry AMD include the presence of drusens that begin to enlarge. Another symptom is blurry areas in central vision. A symptom of Wet AMD is seeing straight lines as wavy ones.

 A visual acuity test can help an eye care professional determine if any central vision is lost. An Amsler grid may also be used to detect AMD. In this test you cover one eye and stare at a black dot that has patterns of straight lines. If these lines appear wavy or are missing then AMD could be present.[2] 

Prevention

There is growing evidence that by improving your diet, you may also improve the health of your eyes. Research has suggested an association between macular degeneration and a high saturated fat diet.

There is also evidence that eating fresh fruits and dark green, leafy vegetables – foods rich in vitamins C and E, selenium, and carotenoids (including beta-carotene, lutein and zeaxanthin) – may delay or reduce the severity of AMD.

Foods to Enjoy

Eat the freshest and brightest fruits and vegetables. Pick the most colorful vegetables and fruits you can find - red, dark green, orange, or yellow. These foods play a key role in keeping your eyes healthy:

 

Carrots  Corn  Kiwi  Pumpkin  Yellow squash  Zucchini  squash  Red grapes  Green peas  Cucumber Butternut  squash  Green bell  pepper  Celery  Cantaloupe  Sweet potatoes  Dried apricots  Tomato and tomato products  Dark green leafy vegetables  Spinach  Kale  Turnips Collard greens ...

Fish

Eating fatty fish such as salmon, tuna or mackerel two to three times per week can slow the progression of age-related macular degeneration (AMD) according to a study published in the British Journal of Ophthalmology.

This research further confirms earlier studies that suggested eating fish can help reduce the risk of getting AMD and demonstrates that some of those already affected by the disease can benefit as well.

Nuts

Nuts not only contain Omega-3 fatty acids, but also copper which can play a role in preventing age-related eye diseases. Even just a handful of nuts at two or three times a week can reduce your risk of AMD.

Foods to Avoid

A high-fat, high-cholesterol diet can lead to fatty plaque deposits in the macular vessels, which can hamper blood flow and increase the risk of AMD. A diet low in fat promotes good eye health. Skip foods and processed baked goods with high-fat content. In addition recent research has indicated that those consuming red meat (10 times a week or more) were at 47% higher risk for macular degeneration.

Vitamins and Supplements

The National Eye Institute’s Age-Related Eye Disease Study (AREDS) found that taking a specific high-dose formulation of antioxidants and zinc significantly reduces the risk of advanced AMD and its associated vision loss. Slowing AMD’s progression from the intermediate stage to the advanced stage will save the vision of many people.

People who should consider taking the combination of antioxidants plus zinc include those who are at high risk for developing advanced AMD. These people are defined as having either:

  1. Intermediate AMD in one or both eyes. Intermediate AMD is defined as the presence of either many medium-sized drusen or one or more large drusen.
  2. Advanced AMD in one eye, but not the other eye. Advanced AMD is defined as either a breakdown of light-sensitive cells and supporting tissue in the central retinal area (advanced dry form), or the development of abnormal and fragile blood vessels under the retina (wet form) that can leak fluid or bleed. Either of these forms of advanced AMD can cause vision loss. Ask you doctor if taking this special formulation is right for you and where you can obtain the specific formula in your country.[3]

Grapes May Help Prevent AMD

Can eating grapes slow or help prevent the onset of age-related macular degeneration (AMD), a debilitating condition affecting millions of elderly people worldwide? Results from a new study published in Free Radical Biology and Medicine suggest this might be the case. The antioxidant actions of grapes are believed to be responsible for these protective effects.[4]

 eResearch by Navid Ajamin -- spring 2012

The Amsler Grid

Video: www.webmd.com/eye-health/video/macular-degeneration-test

Image: www.drchristinachoy.com ; www.feastervillefamilyeyecare.com ; jama.ama-assn.org

Reference:

Related To: Facts About Age-Related Macular Degeneration ; Macular Degeneration and Smoking

Further Information:


 | 2014 © ^ نوشته شده توسط Navid Ajamin | 

Different Types of Glaucoma
There are several different categories of glaucoma which include: Open Angle Glaucoma, Narrow Angle Glaucoma, Congenital Glaucoma and Secondary Glaucoma. 

Effect of GlaucomaOpen Angle Glaucoma
Open Angle Glaucoma is the most common form of glaucoma and is a result of the trabecular meshwork becoming less efficient over time.  In this case, the eye continues to produce the same amount of aqueous humor, but the trabecular meshwork is not able to keep up.  This imbalance of fluid production and drainage results in an excess amount of aqueous fluid.  As the fluid builds up, the intraocular pressure (IOP) elevates.  As a consequence to this elevation in eye pressure, the optic nerve becomes damaged. 

Glaucome vision lossFor most people with open angle glaucoma, there are no perceivable symptoms in the early stages of the disease.  However, as the optic nerve is continually subjected to an environment of increased eye pressure, it becomes damaged.  This damage is eventually perceived as peripheral visual field defects.  If the eye pressure is not monitored or controlled, open angle glaucoma can eventually lead to blindness.

An ideal intraocular pressure is different for each individual.  Some patients are able to tolerate a higher eye pressure while others cannot.  It is important to be followed regularly by your eye doctor to determine an appropriate target IOP and ensure that this pressure is maintained over time. 

Narrow Angle Glaucoma
Narrow Angle Glaucoma is less common than Open Angle Glaucoma.  People who are farsighted (hyperopic) are more susceptible to this form of glaucoma because they typically have smaller eyes, although Narrow Angle Glaucoma can occur in nearsighted eyes.  A smaller eye correlates to more crowding of the structures within the eye.  In a normal eye there is sufficient space between the iris (the colored part of the eye) and the trabecular meshwork.  However, in a crowded eye, the space between the iris and the trabecular meshwork is narrowed. 

The iris controls the amount of light that enters the eye.  Under bright light conditions the iris contracts to cover more space and make the pupil smaller (minimizing the amount of light that enters the eye).  In dark lighting conditions, the iris dilates to allow more light to enter the eye.  In a person with narrow angles, as the pupil dilates the iris can completely block the trabecular meshwork drainage angle.  This can result in a rapid rise in eye pressure and can lead to an angle closure glaucoma attack. 

An individual suffering from an angle closure attack typically experiences a severe headache above the eye brow, eye pain, significant eye redness, the pupil becomes fixed and dilated, the vision is significantly blurred, halos are seen around lights and nausea and vomiting can occur.  An angle closure glaucoma attack is an emergency and must be treated immediately.  Unfortunately, the damage done to the optic nerve during an angle closure glaucoma attack can be significant and is permanent.  In some cases, Angle Closure Glaucoma can present insidiously however, without sudden symptoms.

Preventing Angle Closure
Fortunately, there is a means of preventing angle closure attacks.  Narrow angles can be diagnosed during a routine eye exam.  At that time, the doctor will look at the trabecular meshwork drainage angle through a special contact lens.  This testing, referred to as gonioscopy, allows the doctor to determine the degree of narrowing.  If the angles are very narrow, the doctor may recommend a laser procedure known as Laser Peripheral Iridotomy.  During this in-office (out-patient) procedure, a small hole is created in the iris.  This microscopic hole allows for another route for the aqueous fluid to enter the anterior chamber, and allows the iris to fall away from the drainage angle.  The doctor makes the hole on the top part of the iris that is usually covered by the eyelid. 

As with any surgical procedure, there are some risks to Laser Peripheral Iridotomy.  However, the risks of the procedure are minimal and if the procedure is recommended, the benefit of the procedure in reducing the risk of angle closure glaucoma outweighs the risk of the procedure.  Some of the risks include blurred vision, slight bleeding or inflammation within the eye.  Some people notice a twinkle or flicker of light or shadow image after the procedure.  These symptoms can arise from the affect of light entering the small hole in the iris.  This side effect of the procedure is very unusual; in most cases, the upper eyelid covers the location of the iridotomy and the optical side effect is not perceived.  Occasionally, the procedure needs to be repeated if the iridotomy heals over. 

Congenital Glaucoma
Congenital Glaucoma is a result of the malformation of the trabecular meshwork drainage angle during fetal development.  The defective trabecular meshwork impedes the proper drainage of the aqueous fluid within the eye causing an increase in intraocular pressure.  The elevated eye pressure eventually leads to damage of the optic nerve, which may result in blindness.  For this reason it is imperative that children afflicted by the disease be seen by an ophthalmologist regularly in hopes of preserving as much of the child’s vision as possible.   

Congenital glaucoma is generally diagnosed within the first few months of a child’s life.  Infants with congenital glaucoma often have symptoms of tearing, red eye, light sensitivity and a cloudy appearance of the eye.  In the far majority of congenital glaucoma cases, both eyes are affected by the disease.  Males are more commonly afflicted with this disease than females; however, congenital glaucoma is rare, affecting approximately 0.05% of children.   

Secondary Glaucoma
Secondary glaucoma is an acquired form of glaucoma and may present itself as open angle or angle closure glaucoma.  This type of glaucoma can be a result of trauma, inflammatory diseases, tumors or use of corticosteroids.  Secondary glaucoma may be temporary. 

Traumatic Secondary Glaucoma
In the circumstance of either blunt or penetrating ocular trauma, the trabecular meshwork can be damaged.  This damage leads to the trabecular meshwork inefficiently draining the aqueous fluid out of the eye.  As a result, the amount of aqueous fluid in the eye builds and increases the intraocular pressure.  This increase in eye pressure leads to damage of the optic nerve.  Eventually, the optic nerve damage results in visual field defects, and in some cases blindness. 

Inflammatory Glaucoma and Steroid Responders
Inflammatory diseases such as uveitis can also lead to secondary glaucoma.  Additionally, most cases of uveitis are treated with corticosteroids.  Unfortunately, one of the side effects of corticosteroid use can be a significant increase in intraocular pressure.   This cyclic condition is often a tight-rope-walk for the ophthalmologist to effectively treat the ocular inflammation while trying to maintain an adequate intraocular pressure. 

Pseudoexfoliative Glaucoma
One of the more common forms of secondary glaucoma is referred to as pseudoexfoliation glaucoma.  This type of secondary glaucoma occurs when the eye forms material that can affect the drainage angle.  Like a clogged sink, the fluid is unable to properly drain and fluid accumulates within the eye.  This accumulation of fluid can lead to an increase in eye pressure and eventually damage the optic nerve.

Pigmentary Glaucoma
Similarly, pigmentary glaucoma is another form of secondary glaucoma.  Pigmentary glaucoma is a result of the iris pigment breaking off.  These pigment granules can then clog the drainage angle and induce glaucoma.

Neovascular Glaucoma
Neovascular glaucoma is another form of secondary glaucoma.  This form of glaucoma typically affects individuals with diabetes, or eyes that have circulation problems in the retina or in the arteries that supply the eye.  Neovascularization refers to the new growth of abnormal blood vessels.  The new blood vessels can block the trabecular meshwork and lead to high eye pressure.  This form of glaucoma can be difficult to treat.

ICE Syndrome
ICE is an acronym for, “IridoCorneal Endothelial” syndrome.  This is a very rare form of glaucoma that typically affects one eye.  The condition occurs when the endothelial layer (the most inner layer) of the cornea grows over the trabecular meshwork and across the surface of the iris.  This causes an increase in intraocular pressure and leads to damage of the optic nerve.  These abnormal endothelial cells form adhesions that attach the iris to the cornea, which in turn blocks the drainage angle further.

Reference: www.ocvermont.com


 | 2014 © ^ نوشته شده توسط Navid Ajamin | 

Most people get along just fine without true binocular vision. Some do have some difficulty with certain tasks under certain situations. Driving a motor vehicle, especially if the left eye is blurred or otherwise unused, can sometimes be troublesome. Threading a needle is chore. Some sports need good binocular vision as does viewing holographs.! A young child who is delayed in learning to walk or, later, bumps into things (more than normal) should be examined by an eye doctor, preferably an optometrist or someone who understands and can test binocular function. Sometimes there¹s a fairly straightforward diagnosis and management plan. There are a number of vision system causes for loss of binocular function. It is possible, although much more rare, for higher level neurological dysfunction to be the culprit. These would be problems within the brain or the connections between the eyes and the visual processing center in the brain.

What are the causes for loss of binocular vision?

There are number of causes for the lose of binocular vision. The two primary issues are amblyopia and strabismus.[1]

What is Binocular Vision?

Usually the brain gets images from both (bi) eyes (ocular) at the same time. The brain combines the two images into one, to make vision. The images that the brain gets from the eyes are however slightly different from each other. The brain uses these small differences to work out how far away an object is. This is called depth perception. It can also help to work out how quickly an object is moving towards or away from a person. This is a type of movement perception.

What causes loss of binocular vision?

There are lots of reasons why binocular vision might become reduced or lost altogether. Reasons include:

  • Reduced vision in one eye
  • Loss of coordination of movement between the two eyes (squint)
  • Problems with the brain comparing images from both eyes [2]

Binocular Vision Problems

Headaches, eyestrain, fatigue, blurred and double vision are common symptoms for someone with a binocular vision problem. A perfectly healthy eye with 20/20 vision can still have a disorder of the focusing system or the extra-ocular muscles. Binocular vision problems can be a major problem for young students and can impact reading and learning. 

Vision therapy can effectively treat and relieve the symptoms of most binocular vision problems. All children should have a professional eye exam before 30 months, to rule out any possible binocular vision problems.[3]

Binocular interaction

Apart from binocular summation, the two eyes can influence each other in at least three ways.

  • Pupillary diameter. Light falling in one eye affects the diameter of the pupils in both eyes. One can easily see this by looking at a friend's eye while he or she closes the other: when the other eye is open, the pupil of the first eye is small; when the other eye is closed, the pupil of the first eye is large.
  • Accommodation and vergence. Accommodation is the state of focus of the eye. If one eye is open and the other closed, and one focuses on something close, the accommodation of the closed eye will become the same as that of the open eye. Moreover, the closed eye will tend to converge to point at the object. Accommodation and convergence are linked by a reflex, so that one evokes the other.
  • Interocular transfer. The state of adaptation of one eye can have a small effect on the state of light adaptation of the other. Aftereffectsinduced through one eye can be measured through the other.[4]

Two Eyes = Three Dimensions (3D)
Each eye captures its own view and the two separate images are sent on to the brain for processing. When the two images arrive simultaneously in the back of the brain, they are united into one picture. The mind combines the two images by matching up the similarities and adding in the small differences. The small differences between the two images add up to a big difference in the final picture! The combined image is more than the sum of its parts. It is a three-dimensionalstereo picture.

The word "stereo" comes from the Greek word "stereos" which means firm or solid. With stereo vision you see an object as solid in three spatial dimensions--width, height and depth--or x, y and z. It is the added perception of the depth dimension that makes stereo vision so rich and special.

Stereo Vision Has Many Advantages
Stereo vision--or stereoscopic vision --probably evolved as a means of survival. With stereo vision, we can see WHERE objects are in relation to our own bodies with much greater precision--especially when those objects are moving toward or away from us in the depth dimension. We can see a little bit around solid objects without moving our heads and we can even perceive and measure "empty" space with our eyes and brains.[5]

Image: www.cg.tuwien.ac.at; www.vision3d.com; www.publichealthagency.org ;www.colonyeyecare.com

eresearch by Navid Ajamin H. Spring 2011

Reference:


 | 2014 © ^ نوشته شده توسط Navid Ajamin | 

WHAT IS A CATARACT (CAT-ah-rackt)? 
The word cataract is derived from a Greek word meaning "waterfall" (looking through falling water). Cataracts are most commonly caused by chemical changes within the lens of the eye, which is thought to be part of the natural aging process.[1]

A cataract is a gradual clouding of the eye's natural lens. The formation of a cataract occurs during the normal process of aging. Although cataracts may affect people of any age, they are most common in older adults. Because cataracts form gradually, the symptoms are often difficult to spot. Perhaps you have noticed increased difficulty when driving toward the sun, find it harder to see traffic lights against a bright sky, or find it takes longer for your vision to return to normal after passing an oncoming set of bright headlights.

Symptoms include reduced depth perception, diminished color perception, annoying glare in sunlight, and poor night vision. Headaches, eye fatigue, burning, and watering of the eyes when exposed to bright light are also some other symptoms attributed to cataracts.[2]

More than half of all Americans age 65 and older have cataracts.

What Causes Cataracts?

The eye functions much like a camera. Light rays enter the eye, passing through the cornea, the aqueous humor -- transparent fluid in the front of the eye -- and then the pupil and into the lens. The lens bends the light rays to focus objects onto the retina lining the back of the eye. From there, the image passes through the retinal cells, into the optic nerve, and finally to the back of the brain which process the images.

Cataracts occur when there is a buildup of protein in the lens that makes it cloudy. This prevents light from passing clearly through a the lens, causing some loss of vision. Since new lens cells form on the outside of the lens, all the older cells are compacted into the center of the lens resulting in the cataract.

Types of cataracts include:

Age-related cataracts. As the name suggests, this type of cataract develops as a result of aging.

Congenital cataracts. Babies are sometimes born with cataracts as a result of an infection, injury, or poor development before they were born, or they may develop during childhood.

Secondary cataracts. These develop as a result of other medical conditions, like diabetes, or exposure to toxic substances, certain drugs (such as corticosteroids or diuretics), ultraviolet light, or radiation.

Traumatic cataracts. These form after injury to the eye.

Other factors that can increase a person's risk of developing cataracts include cigarette smoke, air pollution, and heavy alcohol consumption.

What Are the Symptoms of Cataracts?

Cataracts usually form slowly and cause few symptoms until they noticeable block light. When symptoms are present, they can include:

  • Vision that is cloudy, blurry, foggy, or filmy.
  • Progressive nearsightedness in older people often called "second sight" because they may no longer need glasses.
  • Changes in the way you see color because the discolored lens acts as a filter.
  • Problems driving at night such as glare from oncoming headlights.
  • Problems with glare during the day.
  • Double vision.
  • Sudden changes in glasses prescription. [3]

 

Image:www.campuseyegroup.com Related To: Cataract Causes, incidence, and risk factors

Reference:


 | 2014 © ^ نوشته شده توسط Navid Ajamin | 

Diplopia is the medical term for double vision. It is caused due to defective functioning of the extraocular muscles or a disorder of the nerves that stimulate the muscles. Usually, double vision is a symptom of strabismus, i.e., squint. Strabismus is a misalignment or deviation of the two eyes. All types of strabismus do not give rise to double vision. A person suffering from diplopia loses his ability to walk, read, and do routine activities.

 

 

The brain of a young child with strabismus (paralytic, congenital, or accommodative) tends to suppress the unwanted second image produced by misaligned strabismic eye so that only one image is seen by the child. This natural attempt of the body to prevent double vision leads to poor vision in the affected eye. The only symptom observed in diplopia is the visualization of two images of the same object.

 

Usually, there is paralysis of one or more of the eye muscles in diplopia. So, movement of the eye in a particular condition is not possible. Double vision can be overcome by tilting or turning the head. Image separation can occur temporarily due to a growth in the eyelid pressing upon the front of the eye ball. The eyeballs themselves may protrude (exophthalmos) as a result of overfunctioning of the thyroid gland (hyperthyroidism). Swelling and scarring within the eyelid can also produce double vision. In rare cases, an eye abnormality can cause diplopia. For example, a dislocated lens will result in the passing of light rays only partly through itself with the rest spreading over the surrounding area. This leads to the formation of two images on the retina.

 

The management of diplopia may entail the use of prisms (optical devices used to deviate images), orthoptics (treatment by exercises to strengthen the eye muscles), occlusion (covering the abnormal eye), and eye muscle surgery. these may be tried out alone or in various combinations, the basic goal being to restore binocular vision, where the person sees only a single image. The cause of strabismus should be ascertained early in the case of children, so that corrective treatment can be started immediately. In adults, double vision needs to be treated urgently to avoid the progression of a probable tumor, aneurysm, or neurological abnormality. If the diplopia is a result of some severe underlying pathology, the cause should be treated first. Surgical intervention should always be the last resort.

doubvision

 

Diplopia may be preventable in certain cases. For example, post-traumatic double vision can be avoided by wearing a seat belt when driving a four-wheeler and a helmet when riding a two-wheeler. This will reduce the impact of the injury. While indulging in any sports activity, it is advisable to wear protective headgear and glares to protect the head and the eyes respectively. Similarly, if your occupation exposes you to the risk of suffering an eye injury, special precautions must be taken. If you are a diabetic, you should ensure that you maintain your blood sugar levels close to normal in order to avoid diplopia caused by nerve damage.

 

eResearch by Navid Ajamin -- 2011

 

Reference: www.healthizen.com    Stay Healthy.Everyday.

 

Image:www.wrongdiagnosis.com www.jeffreymd.com


 | 2014 © ^ نوشته شده توسط Navid Ajamin | 

Glaucoma is a multi-factorial, complex eye disease with specific characteristics such as optic nerve damage and visual field loss. While increased pressure inside the eye (called intraocular pressure or IOP) is usually present, even patients with normal range IOP can develop glaucoma.

There is no specific level of elevated eye pressure that definitely leads to glaucoma; conversely, there is no lower level of IOP that will absolutely eliminate a person’s risk of developing glaucoma. That is why early diagnosis and treatment of glaucoma is the key to preventing vision loss.

Eye pressure is measured in millimeters of mercury (mm Hg). Normal eye pressure ranges from 12-22 mm Hg, and eye pressure of greater than 22 mm Hg is considered higher than normal. When the IOP is higher than normal but the person does not show signs of glaucoma, this is referred to as ocular hypertension.

High eye pressure alone does not cause glaucoma. However, it is a significant risk factor. Individuals diagnosed with high eye pressure should have regular comprehensive eye examinations by an eyecare professional to check for signs of the onset of glaucoma.

In the past, eye care professionals sometimes referred to a person with an elevated IOP as a glaucoma suspect, because of the concern that the elevated eye pressure might lead to glaucoma. However, the term glaucomasuspect is usually reserved today to describe a person who has suspicious optic nerve cupping in the setting of normal IOP and normal visual fields. 

In the majority of cases, vision loss usually occurs when the eye pressure is too high for the specific individual and damages the optic nerve. Any resultant damage cannot be reversed. In eyes with glaucoma, peripheral (side) vision is affected first. The changes in vision may be so gradual that they are not noticed until a lot of vision loss has already occurred.

In time, if the glaucoma is not treated, central vision will also be decreased and then lost — this is how blindness from glaucoma is most often noticed. The good news is that glaucoma can be managed if detected early, and with medical and/or surgical treatment, most people with glaucoma will not lose their sight.

If you are at higher risk for glaucoma, you should have a thorough eye exam every one or two years after age 35. If you are diagnosed with glaucoma, it is important to work with your eye doctor and carefully follow your prescribed treatment. Glaucoma medications will only work if they are taken exactly as advised by your doctor, so it is important to follow your medication regimen carefully.

Image:www.metwesteyecentre.com.au/Images/Image/news/watery/Glaucoma_adv.jpg

Reference: www.glaucoma.org/learn/glaucoma_insigh_1.php

Related To: Childhood Glaucoma ; Types of Glaucoma ; Glaucoma Facts and Stats


 | 2014 © ^ نوشته شده توسط Navid Ajamin | 

شايد بتوان گفت بينائى مهم‌ترين حس انسان است. نه تنها به اين علت که در ارتباط با محيط خارج از بدن، نقش مهمى دارد، بلکه از اين‌رو که اختلال ديد، سبب کاهش يادگيرى نيز مى‌شود. شخص با حس بينائى مى‌تواند از خود محافظت کند، تعادل خود را نگه‌دارد، خلاقيت داشته باشد و بالاخره از ديدن محيط اطراف لذت ببرد. لذا از چشم‌ها بايد نهايت مواظبت به‌عمل آمده و براى بهداشت آن به نکات زير توجه گردد:  

- هرگز نبايد دست آلوده را به چشم ماليد. دست و صورت خصوصاً دست‌ها بايد مرتب با آب و صابون شسته شود. از شستن دست و صورت در آب‌هاى آلوده و کثيف، جداً بايد خوددارى گردد.   
 
 - بايد از حوله و دستمال شخصى و تميز استفاده کرد و هرگز حوله و دستمال ديگران را مورد استفاده قرار نداد.   
 
 - مطالعه بايستى در نور کافى انجام گيرد و از خواندن نوشته‌هاى خيلى‌ريز خوددارى شود.   
 
 - به‌هنگام مسافرت با اتومبيل و ساير وسايط ‌نقليه، حتى‌المقدور از مطالعه خوددارى شود.   
 
 - فاصله چشم از کتاب بايد حدود ۳۰ سانتى‌متر و زاويه کتاب نسبت به سطح مورد مطالعه ۴۵ تا ۷۰ درجه باشد.   
 
 - از خيره‌شدن به نور شديد، مانند خورشيد و لامپ‌هاى پرنور خوددارى شود. هم‌چنين در مقابل آفتاب، باد، گرد و خاک، از چشم‌ها محافظت شود.   
 
  - براى خواب و استراحت، اتاق بايد تاريک باشد تا اعصاب چشم به‌خوبى استراحت کند.   
 
 - مصرف غذاهاى داراى ويتامين A و پروتئين در حفظ سلامت چشم اهميت به‌سزائى دارد.   

  اختلالات بينائى در سلامت دانش‌آموز و پيشرفت تحصيلى او اثر زيادى دارد و بايد مورد توجه مسئولان آموزشگاه قرار گيرد. آموزگار، مدير، پزشک، مربى بهداشت در تأمين سلامت بينائى شاگردان مسئوليت مشترک دارند. آموزگار به‌علت تماس دائمى با شاگردان، بهتر از هر شخص ديگر با توجه دقيق، به خواندن و نوشتن و کار کردن آنها مى‌تواند افرادى را که داراى اختلال يا ضعفى در قوه بينائى هستند، بشناسد و پس از آزمايش، آنها را نزد پزشک هدايت نمايد.

 به‌طور کلى علائمى که شخص با ديدن آن علائم، بايد متوجه اختلالاتى در دستگاه بينائى خود گردد، عبارتند از:   
 
  - اگر اشياء و نوشته‌ها را در فاصله معمولى به‌خوبى نتوان مشاهده نمود و يا هنگام نگاه‌کردن به آنها احساس ناراحتى کرد.   
 
 - اگر در هنگام غروب آفتاب نتوان به‌خوبى ديد.   
 
 - اگر احساس شود که چشم زود خسته مى‌شود.   
  
 - اگر گاهى سردرد، به‌خصوص هنگام غروب عارض شود.   
  
 - اگر چشم، خارش و سوزش داشته باشد و يا درد بگيرد.   
  
 - اگر صبح‌ها، هنگام بيدار شدن، در گوشه چشم ترشحاتى جمع شود.   
 
 با مشاهده علائم بالا، لازم است به چشم پزشک مراجعه نموده و دستورات وى را به دقت به‌کار برید.  

 
 
 
 اختلالات بينائى  

  دوربينى، نزديک‌بينى، و آستيگماتيسم، از اختلالات عمده بينائى در دانش‌آموزان به شمار مى‌رود.   
 
 دوربينى  


 
 در افراد دوربين، اشعه‌هاى نورانى که به‌طور موازى به چشم مى‌تابد، در عقب شبکيه، تشکيل تصوير مى‌دهد که اين اختلال گاهى علل ارثى دارد. دانش‌آموزانى که به اين عارضه دچار هستند، چشمان خود را زياد مى‌مالند. در موقع کارهاى ظريف مضطرب و بى‌‌قرار هستند. در موقع خواندن يا نوشتن، سر را دورتر از حد معمول نگاه مى‌دارند. به خواندن يا ديدن کتاب‌هاى مصور تمايلى نشان نمى‌دهند. درد چشم، سردرد، التهاب پلک، تيک صورت و گاهى سرگيجه دارند. براى درمان دوربيني، از عينک‌هاى با عدسى محدب استفاده مى‌گردد.   
 
 نزديک‌بينى  

 
 در افراد نزديک‌بين، اشعه نورانى که به چشم مى‌تابد جلوتر از شبکيه، تشکيل تصوير مى‌دهد. نزديک‌بينى به حالت و عادت کسانى که چشم خود را تنگ مى‌کنند تا بهتر ببينند، اطلاق مى‌شود. فاکتورهائى نظير کار نزديک، کمى‌ نور، کمبود ويتامين‌ها و غيره در ايجاد نزديک‌بينى مؤثر هستند. دانش‌آموزانى که به اين عارضه دچارند، اغلب موقع نگاه‌کردن به دور، گردن مى‌کشند. در موقع نوشتن يا خواندن، سر را از حد معمول نزديک‌تر مى‌برند. گاهى يک چشم را مى‌بندند و با تنگ نمودن چشم ديگر، سعى در تطابق اجسام دارند. سردرد و آب‌ريزى از چشم نيز مشاهده مى‌گردد. براى درمان نزديک‌بيني، از عينک‌هاى با عدسى مقعر مناسب استفاده مى‌گردد.   
 
 آستيگماتيسم  


 
 اين عارضه از عيوب انکسارى چشم است. در اين عارضه، تصوير يک نقطه همان يک نقطه درک نمى‌شود، بلکه از يک نقطه از هر جسم خارجي، دو خط افقى ديده مى‌شود. در اين حالت بعضى از اشعه‌هاى نوراني، يکديگر را روى شبکيه قطع مى‌کنند، در حالى‌که محل تلاقى پاره‌اى ديگر، در جلو يا عقب شبکيه است و تصويرى که ايجاد مى‌کند، زياد روشن و واضح به‌نظر نمى‌رسند. دانش‌آموزان مبتلا به آستيگماتيسم، اغلب سر را به کتاب يا تصوير نزديک مى‌کنند، سردرد دارند و چشم را هنگام مشاهده تصاوير ظريف مى‌مالند. تصحيح چشم آستيگمات اغلب ساده بوده و با استفاده از عدسى استوانه‌ائى که در جهت مناسبى از چشم قرار داده مى‌شود، انجام مى‌گيرد. مگر در بعضى حالات نادر که تصحيح آن بسيار مشکل بوده و گاهى حتى غيرممکن است.

  

Reference: www.pezeshki.net 

Images: asweknowit.net,inmagine.com


 | 2014 © ^ نوشته شده توسط Navid Ajamin | 

Cataracts [1]

Cataracts are a common age-related vision problem. About 20.5 million Americans age 40 and older have cataracts, and the older a person gets the greater the risk for developing cataracts. Women are more likely to develop cataracts than men, and African Americans and Hispanic Americans are at particularly high risk.

In addition to age, other factors may increase the risk of cataract development. These include:

  • Diabetes
  • Smoking
  • Over-exposure to sunlight

Symptoms

During the early stages, cataracts may have little effect on vision. Symptoms vary due to the location of the cataract in the eye (nuclear, cortical, or posterior subcapsular). Depending on the type and extent of the cataract, patients may experience the following symptoms:

  • Cloudy vision
  • Double or blurry vision
  • Glare and sensitivity to bright lights
  • Colors appear faded
  • Difficulty reading due to reduced black-white contrast [2]
  • Sudden nearsightedness.
  • Changes in the way you see color, especially yellow.
  • Problems driving at night because oncoming headlights are distracting.
  • Problems with glare.
  • Sudden temporary improvement in close-up vision.

Types of cataracts include:

  • Age-related cataracts. As the name suggests, this type of cataract develops as a result of aging.
  • Congenital cataracts. Babies are sometimes born with cataracts as a result of an infection they had before they were born, or they may develop during childhood.
  • Secondary cataracts. These may develop as a result of other diseases, like diabetes, or long-term exposure to toxic substances, certain medications (such as corticosteroids or diuretics), ultraviolet light, and radiation.
  • Traumatic cataracts. These can form after injury to the eye.

Reference:

External links:


 | 2014 © ^ نوشته شده توسط Navid Ajamin | 

Normal Eye

In the normal eye, light rays pass through the cornea, pupil, and lens and focus directly on the retina.  When the cornea fails to focus light rays directly on the retina, refractive errors such as myopia, hyperopia, and astigmatism occur.

Myopia

Myopia, or nearsightedness, occurs when the curvature of the cornea is too steep or the eyeball is too long.  Therefore, light rays entering the eye focus in front of the retina.  This results in blurred vision at distance.

Hyperopia

Hyperopia, or farsightedness, occurs when the curvature of the cornea is too flat or the eyeball is too short.  Therefore, light rays entering the eye focus in back of the retina.  This results in blurred vision at near.

Astigmatism

Astigmatism occurs when the curvature of the cornea is irregularly shaped, like the shape of a football.  Therefore, light rays entering the eye focus at two different foci, causing blurred or distorted vision at distance and near.  Astigmatism can occur alone or in conjunction with myopia and hyperopia.

Presbyopia

Presbyopia is a vision condition in which the crystalline lens loses its flexibility or elasticity, making it difficult to focus on near objects. Generally, presbyopia becomes noticeable in the early to mid-40s. Presbyopia is an unpreventable age-related process.  To help alleviate symptoms of presbyopia, reading glasses, bifocals, progressive lenses, and multifocal contact lenses can be prescribed.

Dry Eye Syndrome

Dry eye syndrome is a physical condition in which the front of the eye becomes dry.  Symptoms of dry eyes will affect the majority of people at some time.  Patients with dry eyes often report feelings of sandy, gritty, burning, tearing, and itchiness in the eye.  Other symptoms include fluctuation in vision, contact lens intolerance and recurrent infections.  Symptoms may worsen in hot and dry climates and can become more irritated by smoke, wind, and air conditioned environments.

Achieving relief from the symptoms of dry eye is easy with dry eye therapy.  Therapy may be as simple as using over the counter artificial tears, but may be complex to involve the use of prescription medications and/or punctal plugs.  A dry eye therapy plan is covered by most major medical insurances and can be easily implemented to help relieve the pesky ailments of dry eyes.

Allergy and Infections

Red eyes that itch and burn are commonly related to an allergy or in worse cases, an infection.  Allergies are common and often present symptoms similar to those of dry eyes, but will definitely become more prevalent during hay fever season.  Irritations caused by allergies can be alleviated with prescription eye drops.

When allergy-like symptoms are accompanied with pain or discomfort, eye secretions, vision loss, and light sensitivity, it may be due to an eye infection.  Infections of the eyes may result from many scenarios, such as eye abrasions from injuries, foreign bodies, or contact lens wear.  Symptoms of an emerging infection can be easily dismissed for an allergy or dry eye, hence it is important that all patients seek immediate care for any suspicious redness, pain, or sudden loss of vision.

Cataract

Cataract is the clouding of the eye’s natural crystalline lens.  This loss of transparency decreases the amount of light that can reach the retina, resulting in overall blurriness of images.  Signs and symptoms of cataract include: blurry, hazy vision, reduced intensity of colors, increased sensitivity to glare, increased difficulty with night vision, and changes in the eye’s refractive error.  Cataracts are typically due to age-related changes in the natural lens.  Other precipitating factors may include: ultraviolet radiation exposure, diabetes, corticosteroid use, smoking, high alcohol consumption, and certain nutrient deficiency.  Recent studies have shown that antioxidants (e.g. vitamin C, vitamin E, carotenoids) may decrease cataract formation.


Glaucoma

Glaucoma is an eye disease caused by an increased pressure in the eye.  This can damage the optic nerve that transmits visual information to the brain, resulting in the loss of vision.  Glaucoma is the second leading cause of blindness in the U.S.  Individuals over the age of 40, individuals with a family history of glaucoma, and African Americans are at an increased risk of developing glaucoma. Other risk factors for the development of glaucoma include: thinner corneas, systemic vascular conditions (e.g. diabetes, hypertension, heart disease), prolong corticosteriod use, high myopia, chronic ocular inflammation, and ocular trauma.


Macular Degeneration

Macular degeneration (MD) is the leading cause of blindness in Americans over the age of 55.  MD causes a deterioration and loss of photoreceptors and other cells in the macula, the part of the retina responsible for sharp, clear central vision.  Because only central vision is usually affected, people rarely go blind from the disease.  However, MD can sometimes make it difficult to read, drive, or perform other daily activities that require fine, central vision.  Most people with MD have the dry form, for which there is no known treatment. The less common wet form may respond to laser procedures, if diagnosed and treated early.  A major National Eye Institute study (AREDS) indicates that certain nutrients such as beta carotene (vitamin A) and vitamins C and E may help prevent or slow progression of MD

Retinal Detachment

The retina is the light-sensitive tissue that lines the inside back wall of the eye.  In retinal detachment, the retina is separated from its underlying supportive tissue, depriving it from nutrients and oxygen.  The longer the retina is detached, the greater the risk of permanent vision loss. Retinal detachment, thus, is a medical emergency requiring prompt surgical treatment to preserve vision.  Warning signs of retinal detachment include: floaters, flashes of light, a sudden decrease in vision, and a shadow or curtain over the vision.  Risk factors for retinal detachment include: high myopia, previous severe eye injury/trauma, family history of retinal detachment, and previous history of retinal detachment in the other eye.


Reference: www.holbert.com


 | 2014 © ^ نوشته شده توسط Navid Ajamin | 

 

Light sensitivity, or photophobia, is an intolerance of light. Some only feel discomfort from bright lights, while others in extreme cases can not stand any type of light. Sources can range from sunlight, fluorescent light, incandescent light or flames of candles or fires. Some people tend to squint or close their eyes if their sensitivity is too strong. There are many different reasons why someone could have a sensitivity to lights, but the biggest issue is the underlying cause, as photophobia is a symptom, not a condition or disease. Photophobia is known to happen to all ages, young and old.

Symptoms of Photophobia

There are a few obvious symptoms to recognize your sensitivity to light has increased, such as:

  • Discomfort
  • Need to close eyes
  • Need to squint
  • Burning
  • Excessive tearing

In some cases, there might not be any sort of symptoms except the sensitivity to light itself. People have reported nothing one day, then sensitivity the next day. Each individual is unique and experiences different symptoms. Again, it depends on the underlying cause. In other cases, people will suffer many other types of symptoms, depending on the condition or disease that is causing the light sensitivity.

Corning glare-control sunglasses. Glare-control sunglasses, like these by Corning, are helpful if you are sensitive to sunlight or even strong indoor lighting.

Causes of Photophobia

There are several different reasons why someone might be suffering from photophobia or sensitivity to light. It’s not a disease, disorder, problem or condition. In fact, it’s a symptom of many different diseases, disorders, problems and conditions. For example, an infection or inflammation that irritates the eyes can cause photophobia. Also, it can be a symptom of an underlying disease such as a viral illness or a severe headache or migraine.


ادامه مطلب

 | 2014 © ^ نوشته شده توسط Navid Ajamin | 
 

Causes

Vision Disorder

An amino acid called tyrosine is normally converted by the body to the pigment called melanin. Albinism results when the body is unable to convert tyrosine into melanin and distribute it throughout the body.

  • Oxygen-Free Radicals (Oxidants) and Glutathione
  • Radiation and Electromagnetic Waves   
  • Radiation Treatments. 
  • Smoking 
  • Genetic Factors 
  • Systemic Diseases
  • Medications
  • Alcohol

Over the years high sugar level can damage the tiny blood vessels in or on the retina. The longer an individual has had diabetes, the risks of diabetic retinopathy increases.

Diabetic Retinopathy
Diabetic Retinopathy

There are several primary categories of glaucoma. The most common form, primary open angle glaucoma (POAG) is when the main drainage area inside the eye is open and clear for maximum drainage, however the eye pressure remains high.

The exact causes of AMD are still unclear. The dry form of AMD may result from the aging of the macular area of the retina, variations of pigment in the macula, or a combination of the two processes.

Macular Degeneration
Macular Degeneration

Nystagmus may be found at birth, may be induced by trauma to the brain such as a stroke, or can be associated with other neurological disorders.  It is also the result of various forms of albinism.

Nystagmus
Nystagmus

The cause of this disorder is unknown, but it may be inherited. A yet unclear mechanism causes the peripheral vision cells (the rods) to deteriorate. The primary risk factor is a family history of retinitis pigmentosa.

Retinitis Pigmentosa
Retinitis Pigmentosa

Common causes include but are not limited to:

  • Stroke
  • Trauma to the brain as a result of an accident
  • A mass in, on or around the brain or the visual pathway

Common Causes of Traumatic Brain Injuries

  • Stroke
  • Trauma to the brain as a result of an accident
  • A mass in or around the brain or the visual pathway

Common Causes of Retinal Detachments

  • Automobile accidents
  • Injuries incurred during ball-sports such as racquetball or baseball
  • Blunt trauma such as a punch to the eye
 
Reference: www.ocusource.com

 | 2014 © ^ نوشته شده توسط Navid Ajamin | 
 
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