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What happens during an eye exam?

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Updated May 22, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Slit-lamp exam
Question: What happens during an eye exam?
Answer: Having a comprehensive eye exam each year is the best way to enjoy good vision throughout your life. During a comprehensive eye exam, your eye doctor will perform several different tests and procedures to check your vision as well as the overall health of your eyes. A comprehensive eye examination takes about an hour, and it should consist of most of the following parts:

Visual Acuity

A visual acuity test is a measure of how well you see or the sharpness and clarity of your vision. Your eye doctor will ask you to read letters on a chart while standing 20 feet away. The smallest letters you are able to read will be recorded as your acuity.

Your visual acuity may be written as 20/20 if your vision is normal. If your vision is reduced, it might be recorded as less than 20/20, such as 20/100.

If you have 20/100 vision, it means that you must be as close as 20 feet to see what a person with normal vision can see at 100 feet. Someone with 20/60 vision would need to move up to 20 feet away to read what a person with normal vision could read from 60 feet away.

Confrontation Visual Fields

A confrontation visual field is a quick check of your basic field of vision, including your central and side (peripheral) vision. Your eye doctor or technician will sit in front of you and ask you to cover one eye. You will then be asked to say when you can see his or her hand as it enters your field of vision from the sides.

Extraocular Movements

This test measures the muscles that control eye movement. It is usually a simple test conducted by moving a pen or small object in different directions of gaze. Restrictions, weaknesses or poor tracking of visual objects are often uncovered.

Pupillary Tests

Pupillary reactions (the way your pupils dilate and constrict in response to light) can reveal a lot about the health of the eyes and of your body. The nerves that control the pupil travel through a long pathway within the body. Certain pupillary reactions can reveal neurological problems, including some serious conditions. Your pupil reactions are tested with a very bright light directed toward one or both of your eyes. Your doctor may focus on one eye or swing the light back and forth to study the ways your pupils change.

Cover Test

The cover test is performed to measure how well your eyes work together. The cover test is a simple test in which the doctor asks you to fixate on a near or distant object. He covers one eye, pauses, and then uncovers it. He is evaluating your eye as it is uncovered, as it refixates on the target.

The cover test helps to detect crossed eyes (strabismus), lazy eye (amblyopia) or a decrease in depth perception.

Retinoscopy

Retinoscopy is a test that gives your eye doctor a way to measure refraction. Usually performed early in an exam, retinoscopy provides your doctor a starting point to estimate your prescription for glasses, if needed.

Refraction

Most people remember refraction as the part of an exam in which the doctor asks the patient, "Which lens is better, one or two?" Refraction is a subjective test to measure nearsightedness, farsightedness, astigmatism or presbyopia.

The doctor places an instrument, called a phoropter, in front of your eyes. A series of lens comparisons are shown to you. The doctor will ask you which lens is clearer.

The results of the refraction test are primarily what the doctor uses to develop your final eyeglass or contact lens prescription.

Slit Lamp Examination

Eye doctors use an instrument called a slit lamp, also called a biomicroscope, to examine the front (anterior segment) and back (posterior segment) part of your eye. This is to evaluate the overall health of the eye.

The instrument magnifies your eyes many times and uses a bright light to illuminate the eye structures. Each part of your eye, including your eyelids and eyelashes, conjunctiva, cornea, iris, crystalline lens and anterior chamber, is examined in a methodical manner to reveal any defects or diseases. Cataracts can be diagnosed using the slit lamp.

Tonometry

Tonometry is the measurement of the eye’s pressure, better known as IOP, or intraocular pressure. Your eye doctor will put a drop of anesthetic into your eye. He will then place a small amount of fluorescein (yellow dye) into your eye. A small device called a tonometer is moved close to your eye so that it gently touches the cornea, measuring the pressure of your eye. If your eye pressure is higher than normal, your risk of developing glaucoma increases. (Some physicians prefer to measure eye pressure with the "air puff" test in which a non-contact tonometer (NCT) determines eye pressure with a painless puff of air.)

Dilated Fundus Examination

The dilated fundus examination is usually the last step in a comprehensive eye examination. Your eye doctor will administer special eye drops to dilate your pupils. This increases the size of your pupil, giving your doctor a larger window in which to inspect your internal eye health. The doctor is able to examine the vitreous, optic nerve, blood vessels, macula and retina.

An instrument called a binocular indirect ophthalmoscope (BIO) is worn on the doctor’s head. This frees the doctor’s hands in order to use a powerful lens to focus light emitted from the ophthalmoscope into your eye. With this instrument, the image is a bit smaller but the field of view is much larger, allowing the doctor to view your entire retina.

The dilated fundus examination is a crucial part of an eye exam, as many eye diseases can be detected during the test.

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