Why is comprehensive eye examination so important?
You might be wondering if you really do need regular eye examinations if you don’t feel any abnormalities in your eyes or your vision. The truth is, some eye diseases do not present with any symptoms until they are in a very advanced stage, when it may be too late for effective treatment. It is therefore recommended that you have at least one complete eye checkup every two years, and at least one every year if you're forty and older. The risks of many eye diseases increase with age. For example, glaucoma is found in about 0.05% of the people over forty who do not have any eye symptoms. That is a low percentage, but the consequences of glaucoma are severe and permanent. Don’t take that chance!<
A comprehensive eye exam consists of 4 parts:
1. Visual Acuity
The first test you get in an eye examination is the measurement of your visual acuity, which is how well your eyes can distinguish small details of distant objects, by reading a chart of numbers of decreasing sizes. The result is expressed in a 20-foot denomination compared to the general population. For example, 20/200, or twenty-two-hundred visual acuity would mean that the smallest line of numbers you can read at 20 feet can be read by most people at 200 feet. And that means you cannot see as well as most people do.
Passing a driver’s license examination requires at least 20/40 visual acuity, so 20/40 is considered legally “normal” vision, while 20/20 is regarded by most people as “perfect vision”. If your unaided vision is not 20/20, the next step in an eye exam is to do refraction, or the detection and measurement of focusing defects, such as nearsightedness, farsightedness, and astigmatism.
If your unaided vision is not 20/20, a test called “refraction” is performed to find out if you have any focusing defects and to measure them if you do. Focusing defects include nearsightedness, farsightedness, and astigmatism, collectively termed “refractive errors”. These occur when the focusing power of the eye does not match up with the eye’s length. For more information, please see our section on Refractive Errors.
A technician may use a computerized machine called the autorefractor to estimate your refractive errors and use different lenses to try to come up with the combination that would yield the best vision in each eye. These results would be used by the ophthalmologist in deciding whether prescription eyeglasses are needed in your case, and in the actual prescribing of the optical aids.
3. Eye measurements
A measurement is taken of the pressure inside the eye. This is to screen for glaucoma, a condition where the eye cannot withstand its own pressure. Most people with glaucoma have no symptoms, and most have a pressure that is higher than normal, which ranges between 10 and 20 millimeters of mercury (mmHg). Any measurement over 20 mmHg should alert the eye doctor and lead to more specific tests that would verify the presence of the disease. The eye pressure can be measured in a variety of ways, with varying levels of accuracy.
4. Eye Health Check
The final part of an eye checkup is the examination by your eye doctor, an ophthalmologist. Your doctor will look at the results of all the tests taken previously, perform a detailed examination of the eyes with a special microscope, and summarize the checkup. He or she may request additional tests for specific diseases if warranted, prescribe visual aids such as eyeglasses, start treatment for any problems found during the examination, or refer you to an appropriate sub-specialist.