What is a Comprehensive Eye Exam?
Optometrists and ophthalmologists 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.
A comprehensive eye exam can take an hour or more, depending on the doctor and the number and complexity of tests required to fully evaluate your vision and the health of your eyes.
Here are eye and vision tests that you are likely to encounter during a routine comprehensive eye exam:
Visual Acuity Test Among the first tests performed in a comprehensive eye exam are visual acuity tests that measure the sharpness of your vision. These usually are performed using a projected eye chart to measure your distance visual acuity and a small, hand-held acuity chart to measure your near vision.
Color Blindness Test A screening test that checks your color vision often is performed early in a comprehensive eye exam to rule out color blindness. In addition to detecting hereditary color vision deficiencies, color blind tests also can alert your eye doctor to possible eye health problems that may affect your color vision.
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, your eye doctor will have you focus on a small object across the room and then he or she will cover each of your eyes alternately while you stare at the target. While doing this, your eye doctor will assess whether the uncovered eye must move to pick up the fixation target, which could indicate strabismus or a more subtle binocular vision problem that could cause eye strain or amblyopia ("lazy eye"). The test is then repeated up close.
Retinoscopy Your eye doctor may perform this test early in the eye exam to obtain an approximation of your eyeglass prescription. 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," your 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, your doctor is able to "ballpark" your prescription — sometimes right on the money! This test is especially useful for children and patients who are unable to accurately answer the doctor's questions.
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 your eye doctor to get a highly magnified view of the structures of your eye to thoroughly evaluate your eye health and detect any signs of infection or disease. During this test, your 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 your eye in turn. He or she will first examine the structures of the front of your eye (lids, cornea, conjunctiva, iris, etc.). Then, with the help of a special high-powered lens, your doctor will view the inside of your eye (retina, optic nerve, macula and more). A wide range of eye conditions and diseases can be detected with slit-lamp examination, including cataracts, macular degeneration, corneal ulcers, diabetic retinopathy, etc.
The Glaucoma Test Glaucoma tests have several variations, all designed to measure the pressure inside your eyes. A common glaucoma test is the "puff-of-air" test, technically known as non-contact tonometry, or NCT. (This test was immortalized on the hit TV show Friends, when Rachel couldn't sit still for it.) For NCT, the test begins with you putting your chin on the machine's chin rest. While you look at a light inside the machine, the doctor or a trained assistant will puff a small burst of air at your open eye. It is completely painless, and the tonometer does not touch your eye. Based on your eye's resistance to the puff of air, the machine calculates your intraocular pressure (IOP). If you have high eye pressure, you may be at risk for or have glaucoma. Another type of glaucoma test is performed with an instrument called an applanation tonometer. The most common of several versions of this instrument is mounted on the slit lamp. For this test, your eye doctor will put yellow eye drops in your eye to numb it. Your eyes will feel slightly heavy when the drops start working. This is not a dilating drop — it is a numbing agent combined with a yellow dye that glows under a blue light. Then the doctor will have you stare straight ahead into the slit lamp while he or she gently touches the surface of your eye with the tonometer to measure your IOP. Like NCT, applanation tonometry is painless. At most, you may feel the tonometer probe tickle your eyelashes. The whole test takes just a few seconds. You typically have no warning signs of glaucoma until you already have significant vision loss. For this reason, routine eye exams that include tonometry are essential to rule out early signs of glaucoma and protect your eyesight. Pupil Dilation to obtain a better view of the eye's internal structures, your eye doctor instills dilating drops to enlarge your pupils. Dilating drops usually take about 20 to 30 minutes to start working. When your pupils are dilated, you will be sensitive to light (because more light is getting into your eye) and you may notice difficulty focusing on objects up close. These effects can last for up to several hours, depending on the strength of the drop used. Once the drops have taken effect, your eye doctor will use various instruments to look inside your eyes. You should bring sunglasses with you to your eye exam, to minimize glare and light sensitivity on the way home. If you forget to bring sunglasses, the staff usually will give you a disposable pair. Pupil dilation is very important for people with risk factors for eye disease, because it allows for the most thorough evaluation of the health of the inside of your eyes.
Visual Field Test In some cases, your eye doctor may want to check for the possible presence of blind spots (scotomas) in your peripheral or "side" vision by performing a visual field test. These types of blind spots can originate from eye diseases such as glaucoma. Analysis of blind spots also may help identify specific areas of brain damage caused by a stroke or tumor.
Other Eye Tests In some cases, besides these common tests performed during a standard comprehensive eye exam, your eye doctor may recommend other, more specialized eye tests. Often, such tests are performed by other eye doctors, such as retinal specialists, on a referral basis.