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What To Expect During a
Comprehensive Eye Exam

By Gary Heiting, OD, and Jennifer Palombi, OD

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 Tests

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.

A standard eye chart.

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.

Refraction

This is the test that your eye doctor uses to determine your exact eyeglass prescription.

Manual refraction with a phoropter.

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.

Autorefractors and Aberrometers

Your eye doctor also may use an autorefractor or aberrometer to automatically determine your prescription.

With both devices, a chin rest stabilizes your head while you typically look at a pinpoint of light or other image.

An autorefractor, like a manual refraction, determines the lens power required to accurately focus light on your retina. Autorefractors are especially useful in certain cases such as evaluating young children who may not sit still, pay attention or interact with the eye doctor adequately for an accurate manual refraction.

Studies have shown that modern autorefractors are very accurate. They also save time. The autorefraction takes only a few seconds, and the results obtained from the automated test greatly reduce the time required for your eye doctor to perform a manual refraction and determine your eyeglass prescription.

An aberrometer uses advanced wavefront technology to detect even obscure vision errors based on the way light travels through your eye. Aberrometers primarily are used for custom or wavefront LASIK vision correction procedures, but many eye doctors are now incorporating this advanced technology into their routine eye exams as well.

Slit-Lamp Examination

The slit lamp is an instrument that the eye doctor uses to examine the health of your eyes.

Slit lamp exam of the front of the eye.

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.

Applanation tonometry (glaucoma test).*

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.

In this video, an eye doctor explains the importance of dilated eye exams. (Video: National Eye Institute)

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.

About Contact Lens Fittings

It's important to understand that a comprehensive eye exam typically does not include a contact lens fitting, and therefore you will not be given a contact lens prescription at the end of a routine eye exam.

There is a possible exception: If you wear contacts currently and the lenses were fitted by the same eye doctor who is performing your comprehensive eye exam, he or she may issue you an updated contact lens prescription at the end of your eye exam.

A contact lens exam that includes fitting services typically is done during a subsequent office visit, when your pupils are not dilated. Your contact lens exam may be performed by the same eye doctor who performed your comprehensive eye exam, or it may be done by a different eye care practitioner (ECP).

Generally, it's better to have your eye exam and your contact lens exam performed at the same practice. Sometimes, if you have these exams performed at different locations, the ECP conducting your contact lens fitting will want to repeat certain tests already performed at your comprehensive eye exam. In part, this is done for liability reasons — to verify the accuracy of your eyeglasses prescription and make sure your eyes are healthy enough to wear contacts.

This duplication of effort often will result in additional costs that you would not experience if your eye exam and contact lens exam are performed at the same location.

[Note: Though an eyeglasses prescription cannot be used to purchase contact lenses, the power of your glasses prescription gives your ECP a starting point for determining the power of your contact lenses. For more about the difference between prescriptions for glasses and contacts, read our article, "Are Contact Lens and Eyeglass Prescriptions the Same?"]

If you need or want to go elsewhere for your contact lens exam after having a comprehensive eye exam, be sure to ask if additional fees will be required to repeat testing already performed during your eye exam.

About the Author: Gary Heiting, OD, is senior editor of AllAboutVision.com. Dr. Heiting has more than 25 years of experience as an eye care provider, health educator and consultant to the eyewear industry. His special interests include contact lenses, nutrition and preventive vision care. Connect with Dr. Heiting via Google+.

*Glaucoma tonometer test image from "Seeing for a Lifetime," an educational presentation developed by the Vistakon division of Johnson & Johnson Vision Care, Inc.

[Page updated April 2013]