A comprehensive eye exam includes a variety of brief tests and evaluations to determine the health of your eyes and the quality of your eyesight. Some of the preliminary testing and data gathering will be performed an assistant or technician. But the health evaluation of your eyes, the prescription of your eyeglasses and/or contact lenses, and the analysis of the findings of your exam will always be performed by your eye doctor – either an optometrist (OD) or an ophthalmologist (MD).
Depending on your needs, your eye exam will last anywhere from 30 to 90 minutes. When you make an appointment for your exam, ask how long your exam will be so you can plan your day accordingly. Be aware that your eye doctor may dilate your pupils, which may affect your near vision for a period of time after your exam.
Though each eye exam is unique, the following tests are performed at most complete eye exams. More tests or fewer tests may be performed at your doctor’s discretion.
Interview and Medical History
You will be asked a number of questions about your health, your vision, and your personal and family medical history. This information helps your doctor determine if you are at risk for certain eye diseases and vision disorders. Some of the questions that may be asked include:
- How old are you?
- Are you satisfied with your current vision?
- What specific vision problems (if any) are you having?
- Do you currently wear eyeglasses full-time, part-time, or not at all?
- Do you wear contact lenses?
- Do you have any health problems?
- Do you take any medicines, including non-prescription products?
- Do you have any allergies, including allergies to medicines?
- Does anyone in your immediate family have glaucoma or other eye problems?
- Does anyone in your immediate family have diabetes, hypertension, or other health problems?
Visual Acuity Test
The clarity of your eyesight is called your visual acuity. Your doctor or an assistant will test your visual acuity at distances of approximately 20 feet (distance vision) and 16 inches (near vision). Visual acuity is typically assessed by determining the smallest letters or numbers you can read on a projected or hand-held chart. It is usually performed one eye at a time. The untested eye is covered with a small hand-held plastic paddle called an occluder.
Visual acuity is recorded as a comparative fraction called the Snellen fraction. If you have “20/20” visual acuity, this means you can read the same size letters that a person with perfect vision can read when you are both twenty feet away. If your vision is “20/40,” the smallest letters you can read at 20 feet a person with perfect vision can see at 40 feet. Thus, if the bottom number of the Snellen fraction is larger, your visual acuity is worse. (A person who has 20/80 vision has only half the visual acuity of a person who is 20/40.)
Early in your exam, your eye doctor will examine your eyes and face without any specialized instruments, paying particular attention to the appearance of:
- Your eyelids and face (looking for any unusual skin conditions)
- The base of your eyelashes (looking for evidence of blepharitis)
- The “whiteness” of your eyes (looking evidence of conjunctivitis or other problems)
The external examination alerts your doctor to problems that may need to be investigated further during the exam or require further evaluation by a medical specialist.
Eye Alignment Test
Using an occluder, your doctor will cover and uncover each of your eyes several times as you focus on an object across the room. By observing how much your eyes must move when uncovered to refocus on the object, your doctor can determine if your eyes are properly aligned and how well they work together as a team. The test (called the cover test) is repeated as you look at an object positioned at a normal reading distance.
Proper eye teaming is necessary for clear, comfortable, binocular vision. Poor eye teaming can lead to eyestrain, blurred vision, double vision, strabismus, and amblyopia.
Pupil Response Test
The pupil is the normally circular opening in the eye that is formed by the inner border of the iris (the pigmented structure that gives our eyes their color). The pupil changes in size in response to different lighting conditions and controls the amount of light that reaches the light-sensitive retina at the back of the eye.
Your eye doctor will look closely at the size of your pupils to see if they are the same size and shape. A significant difference in pupil size may indicate a problem with your eyes or parts of the brain.
Next, your eye doctor will direct a bright beam of light alternately at each of your eyes. By observing the change in size of your pupils in response to the light, your doctor can determine if your pupils function normally.
The refraction is the part of the exam when your doctor determines the prescription of your lenses for eyeglasses.
The refraction may be aided by the use of an automated screening instrument called (not surprisingly) an autorefractor. The measurement of your eyes with an autorefractor takes only a few seconds per eye. Today’s autorefractors are so accurate that it will take your eye doctor only a few minutes to refine the autorefractor result by performing a subjective refraction.
For the subjective refraction, your eye doctor will place an instrument called a phoropter in front of your eyes. The phoropter contains thousands of lens combinations that can be manually introduced in front of your eyes one lens at a time. Using the phoropter, your doctor will show you a series of “either/or” lens choices and ask you which of the two lenses makes things look clearer. Based on your responses, your doctor will fine-tune your eyeglasses prescription to give you the clearest, most comfortable vision possible.
During the subjective refraction, don’t be shy about asking your doctor to show you the lens choices more than once. Also, blink frequently to prevent your eyes from drying out or “tearing up” – both can cause blur that will make it more difficult for you to select the best lenses.
In some cases (especially for children who may be farsighted), your eye doctor may use eye drops that dilate the pupil and relax the focusing muscle inside the eye. This focusing muscle (called the ciliary muscle) changes the shape of the lens inside the eye to allow our eyes to focus on near objects. But over-action of this muscle can mask uncorrected farsightedness (especially in children). Certain dilating drops temporarily force this muscle to relax completely (an action called cycloplegia) and thus enable your eye doctor to determine the most accurate prescription for farsightedness.
Slit Lamp Exam of the Anterior Eye
Your eye doctor will use an instrument called a slit lamp (also called a biomicroscope) to take a close look at the surface of your eyes and the anterior portion of the interior of the eye.
The instrument is called a slit lamp because the magnified beam of light it produces can be narrowed to a thin slit. This enables your doctor to see subtle changes in thickness and contour of the cornea and structures inside the eye.
With special stains and filters, the slit lamp can also be used to evaluate the tear film on the cornea to make sure your eyes have sufficient tears for successful contact lens wear. The slit lamp is also used to examine the crystalline lens behind the pupil to determine if cataracts are developing.
Evaluation of Eye Pressure (The Glaucoma Test)
Excessive pressure inside the eye can damage the optic nerve, leading to glaucoma. This serious eye disease can affect people of any age and is a leading cause of blindness.
Eye pressure is typically measured with one of two devices: an automated non-contact tonometer or a manual applanation tonometer.
The non-contact tonometer indirectly measures the pressure inside your eye with puff of air directed at the center of your cornea. Nothing touches your eye but air. The machine determines how much the shape of your cornea is altered when the air strikes it, and converts this measurement to a reading of the pressure inside the eye.
The applanation tonometer is attached to the slit lamp and measures the pressure of the eye by resting a small device directly against the cornea. Your doctor will first apply an eye drop that contains a short-acting anesthetic to decrease the sensitivity of your eye. The tip of the tonometer (about the size of a small pencil eraser) is then gently placed against the center of the cornea and measures the pressure required to flatten a small circular area on the cornea. The measurement takes only a few seconds and you will have no awareness that the tonometer is touching your eye.
Examination of Posterior Eye (Retina and Optic Nerve)
The retina is the light-sensitive inner lining of the back of the eye. The optic nerve transmits the electrical impulses from the retina to the visual cortex of the brain. Evaluation of the retina and optic nerve is important to rule out glaucoma, age-related macular degeneration (AMD), diabetic retinopathy, and other potentially sight-threatening eye conditions.
To get a view of the entire retina, your doctor may apply eye drops that will dilate your pupils. With your pupils dilated, your doctor may use several techniques to examine your retina and optic nerve.
One method requires a hand-held illuminated microscope called a direct ophthalmoscope. Your doctor holds the direct ophthalmoscope up to his/her eye and moves very close to your face to look inside your eye. The direct ophthalmoscope provides a highly magnified view of the optic nerve and specific areas of the retina, including the macula.
A second method requires an instrument called a binocular indirect ophthalmoscope. This is a combination of a light-emitting device worn on the doctor’s head and a large, hand-held lens. Your doctor will hold the lens close to your eye, fully extending his/her arm while directing a beam of light through the lens. The binocular indirect ophthalmoscope provides a wide angle, three-dimensional view of larger areas of the retina.
A third method requires the use of the slit lamp and a smaller hand-held lens. This method provides a more magnified three-dimensional view of the optic nerve and macula.
Though these are the most common tests performed during a routine eye exam, your eye doctor will determine the scope of your exam and what tests need to be performed to provide an accurate diagnosis and treatment.
The fitting of contact lenses requires additional testing and follow-up exams before a contact lens prescription can be written.
In some cases, your eye doctor will feel it’s necessary for you to have additional specialized tests to rule out or treat eye disease or general health problems. These tests may be performed by your eye doctor or may require that you see a specialist. Be sure to listen to your eye doctor carefully at your eye exam so you fully understand your doctor’s recommendations and why additional testing may be required.