Eye exams involve more than testing your vision — and, if you need glasses or contacts, determining how strong your correction should be. Additional tests assess the appearance and function of all parts of your eyes.
This test examines the muscles that control eye movement, looking for weakness or poor control. Your eye doctor looks at your eyes as you move them in six specific directions and as you visually track a moving object, such as a pen.
This test measures how clearly you can see from a distance. Your doctor will ask you to identify different letters of the alphabet printed on a chart positioned usually 20 feet away. The lines of type get smaller as you move down the chart. You cover one eye and read aloud, then cover the other eye and read aloud.
Refraction refers to how light waves are bent as they pass through your cornea and lens. A refraction assessment helps your doctor determine a corrective lens prescription that will give you the sharpest vision. If you don’t need corrective lenses, you won’t have a refraction assessment.
Your doctor may use a computerized refractor to measure your eyes and estimate the prescription you need to correct a refractive error. 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.
Your eye doctor fine-tunes this refraction assessment by asking you to look through a Phoroptor, a mask-like device that contains wheels of different lenses, and judge which combination gives you the sharpest vision. By repeating this step several times, your doctor finds the lenses that give you the greatest possible acuity.
Your visual field is the area in front of you that you can see without moving your eyes. The visual field test determines whether you have difficulty seeing in any areas of your peripheral vision — the areas on the side of your visual field. There are a few different types of visual field tests:
- Confrontation visual field exam. Your eye doctor sits directly in front of you and asks you to cover one eye. You look directly at your eye doctor while he or she moves his or her hand in and out of your visual field. You tell your doctor when you can see his or her hand.
- Tangent screen exam. You sit a short distance from a screen and stare at a target at its center. You tell your doctor when you can see an object move into your peripheral vision.
- Automated perimetry. Your eye doctor uses a computer program that flashes small lights as you look into a special instrument. You press a button when you see the lights.
Using your responses to one or more of these tests, your eye doctor makes a map of your peripheral vision. If you aren’t able to see in certain areas, your eye doctor uses the map to help diagnose your eye condition.
A slit lamp is a microscope that enlarges and illuminates the front of your eye with an intense line of light. Your doctor uses this light to examine the cornea, iris, lens and anterior chamber of your eye.
When examining your cornea, your doctor may use eyedrops containing fluorescein (flooh-RES-ene) dye. The orange dye spreads across your eyes to help your eye doctor detect tiny cuts, scrapes, tears, foreign objects or infections on your cornea. Your eyes’ tears will wash the dye away.
A retinal examination — sometimes called ophthalmoscopy or fundoscopy — examines the back of your eye, including your retina, 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 special eyedrops. The eyedrops may sting briefly and might cause a medicinal taste in your mouth as the medication drains from your tear ducts into your throat.
After administering eyedrops, your eye doctor may use one or more of these techniques to view the back of your eye:
- Direct examination. Your eye doctor shines a beam of light through your pupil and uses an ophthalmoscope to see the back of your eye. Sometimes eyedrops aren’t necessary to dilate your eyes before this exam. You might see afterimages when your eye doctor stops shining the light in your eyes. This is normal and will go away.
- Indirect examination. For this exam you might lie down or recline in a chair. Your eye doctor will hold each eye open and examine it with a bright light mounted on his or her forehead — a bit like a miner’s lamp. This exam lets your eye doctor see your eye in great detail and in three dimensions. Since this light is brighter than that in a direct examination, you are more likely to see afterimages, but they disappear quickly.
- Slit-lamp exam. In this exam your doctor uses the slit lamp along with the ophthalmoscope to look at the back of your eye. The slit lamp reveals more detailed views of the back of your eye than do direct or indirect examinations.
The retinal examination takes five to 10 minutes, but if you’re given eyedrops, their effects won’t wear off for several hours. Your vision will be blurry, and you’ll have trouble focusing your eyes. You may not be able to drive, so make sure you have another way back to work or home. Depending on your job, you might not be able to work until the eyedrops wear off.
Tonometry measures your intraocular pressure — the pressure inside your eyes. It helps your eye doctor detect glaucoma, a disease that causes pressure to build up inside your eyes and can cause blindness. Glaucoma can be treated if it’s caught early.
Methods your eye doctor may use to test your eyes for glaucoma include:
- Applanation tonometry. This test measures the amount of force needed to temporarily flatten a part of your cornea. Fluorescein, the same orange dye used in a regular slit-lamp exam, is usually put in your eye to make your cornea easier to see. You’ll also receive eyedrops containing an anesthetic. Using the slit lamp, your doctor moves the tonometer to touch your cornea. It won’t hurt, and the anesthetic will wear off within two hours.
- Noncontact tonometry. This method uses a puff of air to test the pressure in your eye. No instruments will touch your eye, so you won’t need an anesthetic. You’ll feel mild pressure on your eye, which can be uncomfortable, but it lasts only seconds.
- Pachymetry. This test measures the thickness of your cornea — an important factor in evaluating your intraocular pressure measurement. After applying numbing eyedrops, your eye doctor uses an instrument that emits ultrasound waves to measure your corneal thickness.
Besides these basic evaluations, you may need more specialized tests, depending on your age, medical history and risk of developing eye disease.
For more information on Comprehensive Eye Exams, click here.