What is comprehensive eye exam?
Many people aren’t sure what to expect when they make an appointment with an eye doctor — especially if they’ve never had a comprehensive eye exam before or it’s been many years since their last exam.
Eye doctors 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 comprehensive eye exam:
Visual acuity tests
A standard eye chart.
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 eye 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 ask you to focus on a small object across the room and will then cover each of your eyes alternately while you stare at the target. The test is then repeated with you looking at a near object.
During these tests, your eye doctor will assess whether the uncovered eye must move to pick up the fixation target, which could indicate strabismus or other problem that could cause eye strain or amblyopia (“lazy eye”).
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 asked to focus on a large target (usually the big “E” on the eye chart). 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. This test estimates which lens powers will best correct your distance vision.
Based on the way the light reflects from your eye, your doctor is able to estimate the power of eyeglasses required to correct your vision.
This is the test that your eye doctor uses to determine your exact eyeglass prescription.
During a refraction, the doctor puts the instrument called a phoropter in front of your eyes and shows you a series of lens choices. He or she will then ask you which of the two lenses in each choice looks clearer.
Based on your answers, your eye doctor will continue to fine-tune the lens power until reaching a final eyeglass prescription.
The refraction determines your level of hyperopia (farsightedness), myopia (nearsightedness), astigmatism and presbyopia.
Slit lamp exam
A slit lamp is a binocular microscope (or “biomicroscope”) that your eye doctor uses to examine the structures of your eye under high magnification. It looks somewhat like a large, upright version of a microscope used in a science lab.
During the slit lamp exam, you will be asked to place your forehead and chin securely against the rests on the front of the instrument and your doctor will begin by examining the structures of the front of your eyes — including your eyelids, cornea, conjunctiva, iris, and lens.
With the help of a hand-held lens, your doctor may also use the slit lamp to examine structures located farther back in the eye, such as the retina and optic nerve.
A wide range of eye conditions and diseases can be detected with the slit lamp exam, including cataracts, macular degeneration, corneal ulcers and diabetic retinopathy, etc.
The glaucoma test
Testing for glaucoma typically begins with measuring the pressure inside your eyes.
A common glaucoma test is the “puff-of-air” test, technically known as non-contact tonometry, or NCT.
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.
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 and takes only a few seconds. At most, you may feel the tonometer probe tickle your eyelashes.
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.
In this video, an eye doctor explains the importance of dilated eye exams. (Video: National Eye Institute)
To obtain a better view of the eye’s internal structures, your eye doctor may use dilating drops to temporarily make your pupils larger. 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.
However, modern retinal imaging devices now can allow your eye doctor to capture a high-resolution, wide-angle photograph of your retina without needing to use dilating drops. These images also can be saved so your eye doctor can use them to evaluate the appearance your retina over time.
Other eye tests
In some cases, besides these common tests performed during a 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.