What to Expect From a Comprehensive Eye Exam
By Dr. Jennifer Palombi
Images thanks to Vistakon.*
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Eye doctors use a wide variety of tests and procedures to examine your eyes. These tests range from simple ones, like having you read an eye chart, to complex tests, such as using a high-powered lens to visualize the tiny structures inside of your eyes. Regardless, when you have an eye exam, it will usually take anywhere from half an hour to an hour or more, depending on the doctor, his or her caseload and the number and complexity of tests required for your eyes.
Here are the basic tests that you are likely to encounter during a routine eye exam (your doctor also has dozens of less routine ones at his or her disposal):
Retinoscopy
The eye doctor will often perform this test early in the eye exam in order to obtain an approximation of your prescription from which to start.
In retinoscopy, the room lights will be dimmed and you will be given a large target (usually the big "E" on the chart) to fixate on. As you stare at the "E," the eye doctor will shine a light at your eye and flip lenses in a machine in front of your eyes.
Based on the way the light reflects from your eye, the doctor is able to "ballpark" your prescription — sometimes right on the money! This test is especially useful for children and non-verbal patients who are unable to accurately answer the doctor's questions.
Refraction
This is the test that the eye doctor uses to determine your exact prescription. During a refraction, the doctor puts the instrument called a phoropter in front of your eyes and shows you a series of lens choices. He or she will then ask you which of the two lenses in each choice looks clearer.
Based on your answers, the doctor will continue to fine-tune your power until reaching a final prescription that is then used in your eyeglasses and contacts.Refraction determines your level of farsightedness, nearsightedness, astigmatism and presbyopia.
Autorefractors and Aberrometers
Your eye doctor also may use an autorefractor or aberrometer to automatically determine your prescription. With both devices, a chin rest stabilizes your head while you typically look at a pinpoint of light or other image.
An autorefractor evaluates the way an image is focused on your retina, where vision processing takes place. While autorefractors are very useful in certain cases such as evaluating young children, some studies show that subjective eye exams tend to produce more accurate results. Subjective eye tests and autorefractors may be used together to produce your prescription.
An aberrometer uses advanced wavefront technology to detect even obscure vision errors based on the way light travels through your eye. Aberrometers are used for custom or wavefront LASIK vision correction procedures.
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Cover Test
While there are many ways for your eye doctor to check how your eyes work together, the cover test is the simplest and most common.
During a cover test, the eye doctor will have you focus on a small object at distance and will then cover each of your eyes alternately while you stare at the target. As they do this, eye doctors observe how much each eye has to move when uncovered to pick up the fixation target. This helps them to detect strabismus, or eye turn, which can cause amblyopia, poor depth perception and other binocular vision problems. The test is then repeated up close.
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Slit-Lamp Examination
The slit lamp is an instrument that the eye doctor uses to examine the health of your eyes. The slit lamp, also called a biomicroscope, allows the doctor to get a highly magnified image of the structures of the eye in order to thoroughly evaluate them for signs of infection or disease.
During this test the doctor will have you place your chin on the chin rest of the slit lamp and will then shine the lamp's light at your eye. The doctor looks through a set of oculars (much like a microscope in a science lab) and examines each part of the eye in turn. Your doctor will first examine the structures of the front of the eye (lids, cornea, conjunctiva, iris, etc.). Then, with the help of a special high-powered lens, he or she will view the inside of the eye (retina, optic nerve, macula and more). A whole range of eye conditions and diseases can be detected with slit-lamp examination, including cataracts, macular degeneration, corneal ulcers, diabetic eye disease, ... the list goes on and on.
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Cataracts
