Diagnosis
Either an ophthalmologist or an optometrist can examine patients for cataracts, but only ophthalmologists are qualified to treat cataracts. The differences are in training:
- An ophthalmologist is a physician who specializes in the medical and surgical care of the eye.
- An optometrist is engaged in the practice of eye care but is not a physician and cannot prescribe medication or perform surgery.
The Diagnostic Tests
The eye professional can observe cloudy areas on the lenses with a direct physical examination, even before the cataracts begin to interfere with vision. Cameras can measure the cataract density. Various vision tests are also performed.
Snellen Eye Chart. To determine how clearly a person can actually see, the familiar Snellen eye chart is used, with rows of letters decreasing in size:
- From a specified distance, usually 20 feet, a person reads the letters using one eye at a time.
- If a person can read down to the small letters on the line marked 20-feet, then vision is 20/20 (the norm).
- If a person can read only down through the line marked 40-feet, vision is 20/40; that is, from 20 feet the patient can read what someone with normal vision can read from 40 feet.
- If the large letters on the line marked 200-feet cannot be read with the better eye, even with glasses, the patient is considered legally blind.
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| Visual acuity tests may be performed in many different ways. It is a quick way to detect vision problems and is frequently used in schools or for mass screening. Driver license bureaus often use a small device that can test the eyes both together and individually. |
Other Tests. Other tests are also used either for diagnosis or for surgical assessment:
- To test contrast sensitivity, a chart similar to the Snellen chart is used, on which the letters are the same size but contrast differently with the background.
- Glare sensitivity is tested by having the patient read a chart twice, with and without bright lights.
- Tests of macular function, which evaluate the eye's acute vision center, can help the ophthalmologist determine the expected improvement from surgery.
- The corneal endothelium, a layer of cells lining the cornea, is sensitive to surgical trauma and should be evaluated before any intraocular operation.
- Patients with other eye disorders may require a number of other pre-operative tests.
Limitations of Eye Tests
Although eye tests aid in making a diagnosis for cataracts, results do not always reflect the quality of life and how effectively people function at home:
- Some people with cataracts perform poorly on the tests yet appear to have no difficulty functioning normally day-to-day.
- Others perform well on the tests but insist that their eyesight is bad enough to curtail ordinary activities, such as driving.
Standard eye tests, therefore, may not be useful for determining whether a patient actually needs cataract surgery.
In general, even if cataracts are diagnosed, the decision to remove them should be based on the patient's own perception of vision difficulties and needs and the effect of vision loss on normal activity. The patient should also be aware of all the risks and costs of surgery. In order to determine the quality of life, the patient may be given a questionnaire such as National Eye Institute Visual Function Questionnaire, which asks 39 questions related to vision and daily activities. This test or others may be useful for determining if eye disease is actually impairing the ability to function.
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