An eye exam usually involves these steps:
- You'll be asked about your medical history and any vision problems you might be experiencing.
- Your eye doctor measures your visual acuity to see if you need glasses or contact lenses to improve your vision.
- You'll be given numbing drops in your eyes. Then your doctor measures your eye pressure.
- Your eye doctor checks the health of your eyes, possibly using several lights to evaluate the front of the eye and inside of each eye. To make it easier for your doctor to examine the inside of your eye, he or she will likely dilate your eyes with eyedrops.
- Your eye doctor discusses what he or she found during the exam and answers questions you have about your eyes.
Part of the examination, such as taking your medical history and the initial eye test, may be performed by a clinical assistant.
Several different tests may be performed during the eye exam. The tests are designed to check your vision and to examine the appearance and function of all parts of your eyes.
Eye muscle test
This test evaluates the muscles that control eye movement. Your eye doctor watches your eye movements as you follow a moving object, such as a pen or small light, with your eyes. He or she looks for muscle weakness, poor control or poor coordination.
Visual acuity test
This test measures how clearly you see. Your doctor asks you to identify different letters of the alphabet printed on a chart (Snellen chart) or a screen positioned some distance away. The lines of type get smaller as you move down the chart. Each eye is tested separately. Your near vision also may be tested, using a card with letters similar to the distant eye. The card is held at reading distance.
Light waves are bent as they pass through your cornea and lens. If light rays don't focus perfectly on the back of your eye, you have a "refractive error." Having a refractive error may mean you need some form of correction, such as glasses, contact lenses or refractive surgery, to see as clearly as possible. Assessment of your refractive error helps your doctor determine a lens prescription that will give you the sharpest, most comfortable vision. The assessment may also determine that you don't need corrective lenses.
Your doctor may use a computerized refractor to estimate your prescription for glasses or contact lenses. Or he or she may use a technique called retinoscopy. In this procedure, the doctor shines a light into your eye and measures the refractive error by evaluating the movement of the light reflected by your retina back through your pupil.
Your eye doctor usually fine-tunes this refraction assessment by having you look through a mask-like device that contains wheels of different lenses (phoropter). He or she asks you to judge which combination of lenses gives you the sharpest vision.
Visual field test (perimetry)
Your visual field is the full extent of what you can see to the sides without moving your eyes. The visual field test determines whether you have difficulty seeing in any areas of your overall field of vision. The different types of visual field tests include:
- Confrontation exam. Your eye doctor sits directly in front of you and asks you to cover one eye. You look straight ahead and tell the doctor each time you see his or her hand move into view.
- Tangent screen exam. You sit a short distance from a screen and focus on a target at its center. You tell the doctor when you can see an object move into your peripheral vision and when it disappears.
- Automated perimetry. As you look at a screen with blinking lights on it, you press a button each time you see a blink.
Using your responses to one or more of these tests, your eye doctor determines the fullness of your field of vision. If you aren't able to see in certain areas, noting the pattern of your visual field loss may help your eye doctor diagnose your eye condition.
Color vision testing
You could have poor color vision and not even realize it. If you have difficulty distinguishing certain colors, your eye doctor may screen your vision for a color deficiency. To do this, your doctor shows you several multicolored dot-pattern tests. If you have no color deficiency, you'll be able to pick out numbers and shapes from within the dot patterns. If you do have a color deficiency, you'll find it difficult to see certain patterns within the dots. Your doctor may use other tests, as well.
A slit lamp is a microscope that magnifies and illuminates the front of your eye with an intense line of light. Your doctor uses this device to examine the eyelids, lashes, cornea, iris, lens and fluid chamber between your cornea and iris.
Your doctor may use a dye, most commonly fluorescein (flooh-RES-een), to color the film of tears over your eye. This helps reveal any damaged cells on the front of your eye. Your tears wash the dye from the surface of your eye fairly quickly.
A retinal examination — sometimes called ophthalmoscopy or funduscopy — allows your doctor to evaluate the back of your eye, including the retina, the optic disk and the underlying layer of blood vessels that nourish the retina (choroid). Usually before your doctor can see these structures, your pupils must be dilated with eyedrops that keep the pupil from getting smaller when your doctor shines light into the eye.
After administering eyedrops and giving them time to work, your eye doctor may use one or more of these techniques to view the back of your eye:
- Direct exam. Your eye doctor uses an ophthalmoscope to shine a beam of light through your pupil to see the back of the eye. Sometimes eyedrops aren't necessary to dilate your eyes before this exam.
- Indirect exam. During this exam, you might lie down, recline in a chair or sit up. Your eye doctor examines the inside of the eye with the aid of a condensing lens and a bright light mounted on his or her forehead. This exam lets your doctor see the retina and other structures inside your eye in great detail and in three dimensions.
Screening for glaucoma
Tonometry measures the fluid pressure inside your eye (intraocular pressure). This test helps your eye doctor detect glaucoma, a disease that damages the optic nerve.
Several methods to measure intraocular pressure are available, including:
- Applanation tonometry. This test measures the amount of force needed to temporarily flatten a part of your cornea. You'll be given eyedrops with fluorescein, the same dye used in a regular slit-lamp examination. You'll also receive eyedrops containing an anesthetic. Using the slit lamp, your doctor moves the tonometer to touch your cornea and determine the eye pressure. Because your eye is numbed, the test doesn't hurt.
- Noncontact tonometry. This method uses a puff of air to estimate the pressure in your eye. No instruments touch your eye, so you won't need an anesthetic. You'll feel a momentary pulse of air on your eye, which can be startling.
If your eye pressure is higher than average or your optic nerve looks unusual, your doctor may use a pachometer. This instrument uses sound waves to measure the thickness of your cornea. The most common way of measuring corneal thickness is to put an anesthetic drop in your eye, then place a small probe in contact with the front surface of the eye. The measurement takes seconds.
You may need more-specialized tests, depending on your age, medical history and risk of developing eye disease.