An eye exam involves a series of tests to evaluate your vision and check for eye diseases. Your eye doctor is likely to use various instruments, shine bright lights at your eyes and request that you look through an array of lenses. Each test during an eye exam evaluates a different aspect of your vision or eye health.

An eye exam helps detect eye problems at their earliest stage — when they're most treatable. Regular eye exams give your eye care professional a chance to help you correct or adapt to vision changes and provide you with tips on caring for your eyes. And an eye exam might provide clues to your overall health.

When to have an eye exam

Several factors can determine how frequently you need an eye exam, including your age, health and risk of developing eye problems. General guidelines are as follows:

Children 3 years and younger

Your child's pediatrician will likely check your child's eyes for healthy eye development and look for the most common childhood eye problems — lazy eye, cross-eyes or misaligned eyes. A more comprehensive eye exam between the ages of 3 and 5 will look for problems with vision and eye alignment.

School-age children and adolescents

Have your child's vision checked before he or she enters kindergarten. Your child's doctor can recommend how frequent eye exams should be after that.

Adults

In general, if you are healthy and you have no symptoms of vision problems, the American Academy of Ophthalmology recommends having a complete eye exam at age 40, when some vision changes and eye diseases are likely to start. Based on the results of your screening, your eye doctor can recommend how often you should have future eye exams.

If you're 60 or older, have your eyes checked every year or two.

Have your eyes checked more often if you:

• Wear glasses or contact lenses
• Have a family history of eye disease or loss of vision
• Have a chronic disease that puts you at greater risk of eye disease, such as diabetes
• Take medications that have serious eye side effects

There are three types of eye specialists. Which specialist you choose might be a matter of preference or will depend on the nature of your eye problem.

• Ophthalmologists. These medical doctors provide full eye care, such as performing complete eye exams, prescribing corrective lenses, diagnosing and treating complex eye diseases, and performing eye surgery.
• Optometrists. These doctors provide many of the same services as ophthalmologists, such as performing complete eye exams, evaluating your vision, prescribing corrective lenses, diagnosing common eye disorders and treating selected eye diseases with drugs. If you have a complex eye problem or need surgery, your optometrist can refer you to an ophthalmologist.
• Opticians. They fill prescriptions for eyeglasses, including assembling, fitting and selling them. Some opticians also sell contact lenses. Opticians do not provide eye health evaluations.

Bring your prescription eyewear

If you wear contact lenses or glasses, bring them to your appointment. Your eye doctor will want to make sure your prescription is the best one for you.

Other precautions

Bring sunglasses to wear after your eye exam. If your eyes are dilated during your exam, sunlight or other bright lights can cause discomfort or blurred vision. Also, consider having someone else drive you home.

Before the exam

If you're seeing a new eye doctor or if you're having your first eye exam, expect questions about your vision and general health history. Your answers help your eye doctor understand your risk of eye disease and vision problems. Questions might include:

• Are you having eye problems now?
• Have you had eye problems in the past?
• Do you wear glasses or contacts? If so, are you satisfied with them?
• What health problems have you had in recent years?
• Were you born prematurely?
• What medications do you take?
• Do you have allergies to medications, food or other substances?
• Have you had eye surgery?
• Does anyone in your family have eye problems, such as macular degeneration, glaucoma or retinal detachments?
• Do you or does anyone in your family have diabetes, high blood pressure, heart disease or any other health problems that can affect the whole body?

During the exam

A clinical assistant or technician might do part of the examination, such as taking your medical history and giving the initial eye test. An eye exam usually involves these steps:

• Measurement of your visual acuity to see if you need glasses or contact lenses to improve your vision.
• Measurement of your eye pressure. You'll be given a numbing drop in your eyes. To make it easier for your doctor to examine the inside of your eye, he or she will likely give you eyedrops to dilate your eyes.
• Evaluation of the health of your eyes. After the dilating drops take effect, your eye doctor might use several lights or imaging to evaluate the front of the eye and the inside of each eye.

Your doctor might use several tests to check your vision and the appearance and function of all parts of your eyes.

After the exam

At the end of your eye exam, you and your doctor will discuss the results of all testing, including an assessment of your vision, your risk of eye disease and preventive measures you can take to protect your eyesight.

Different types of eye exams

Eye muscle test

This test evaluates the muscles that control eye movement. Your eye doctor watches as your eyes follow a moving object, such as a pen or small light. He or she looks for muscle weakness, poor control or poor coordination.

Visual acuity test

This test measures how clearly you see. Your doctor asks you to identify different letters of the alphabet printed on a chart or a screen positioned some distance away. The lines of type get smaller as you move down the chart.

Each eye is tested separately. Your near vision also may be tested, using a card with letters held at reading distance.

Refraction assessment

Light waves are bent as they pass through your cornea and lens. If light rays don't focus perfectly on the back of your eye, you have a refractive error. That can mean you need some form of correction, such as glasses, contact lenses or refractive surgery, to see as clearly as possible.

Assessment of your refractive error helps your doctor determine a lens prescription that will give you the sharpest, most comfortable vision. The assessment can also determine that you don't need corrective lenses.

Your doctor may use a computerized refractor to estimate your prescription for glasses or contact lenses. 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 back through your pupil.

Your eye doctor usually fine-tunes this refraction assessment by having you look through a masklike device that contains wheels of different lenses (phoropter). He or she asks you to judge which combination of lenses gives you the sharpest vision.

Visual field test (perimetry)

Your visual field is the full extent of what you can see to the sides without moving your eyes. The visual field test determines whether you have difficulty seeing anywhere in your overall field of vision. Types of visual field tests include:

• Confrontation exam. Your eye doctor sits directly in front of you and asks you to cover one eye. You look straight ahead and tell the doctor each time you see his or her hand move into view.
• Manual testing, including tangent screen and Goldmann exams. You sit a short distance from a screen and focus on a target at its center. You tell the doctor when you can see an object move into your peripheral vision and when it disappears.
• Automated perimetry. As you look at a screen with blinking lights on it, you press a button each time you see a light.

Using your responses to one or more of these tests, your eye doctor determines the fullness of your field of vision. If you aren't able to see in certain areas, noting the pattern of your visual field loss can help your eye doctor diagnose your eye condition.

Color vision testing

You could have poor color vision without realizing it. If you have difficulty distinguishing certain colors, your eye doctor might screen your vision for a color deficiency. To do this, your doctor shows you several multicolored dot-pattern tests.

If you have no color deficiency, you'll be able to pick out numbers and shapes from within the dot patterns. If you do have a color deficiency, you'll find it difficult to see certain patterns within the dots.

For most people, color blindness that's present at birth (congenital) is red-green, meaning you can't distinguish those colors. Most people who develop color blindness as a result of disease, such as glaucoma or optic nerve disease, can't distinguish blue-yellow.

Slit-lamp examination

A slit lamp is a microscope that magnifies and illuminates the front of your eye with an intense line of light. Your doctor uses this device to examine the eyelids, lashes, cornea, iris, lens and fluid chamber between your cornea and iris.

Your doctor may use a dye, most commonly fluorescein (flooh-RES-een), to color the film of tears over your eye. This helps reveal damaged cells on the front of your eye. Your tears wash the dye from the surface of your eye fairly quickly.

Retinal examination

This examination — sometimes called ophthalmoscopy or funduscopy — allows your doctor to evaluate the back of your eye, including the retina, the optic disk and the retinal blood vessels that nourish the retina. Having your pupils dilated with eyedrops before the exam keeps your pupils from getting smaller when your doctor shines light into the eye.

After administering eyedrops and giving them time to work, your eye doctor may use one or more of these techniques to view the back of your eye:

• Direct exam. Your eye doctor uses an ophthalmoscope to shine a beam of light through your pupil to see the back of the eye. Sometimes eyedrops aren't necessary to dilate your eyes before this exam.
• Indirect exam. During this exam, you might sit up or be reclined in the exam chair. Your eye doctor examines the inside of the eye with the aid of a condensing lens and a bright light mounted on his or her forehead. This exam lets your doctor see the retina and other structures inside your eye in great detail and in three dimensions.

Screening for glaucoma

Tonometry measures the fluid pressure inside your eye (intraocular pressure). This is one test that helps your eye doctor detect glaucoma, a disease that damages the optic nerve.

Several methods to measure intraocular pressure are available, including:

• Applanation tonometry. This test measures the amount of force needed to temporarily flatten a part of your cornea. You'll be given eyedrops with fluorescein, the same dye used in a regular slit-lamp examination. You'll also receive eyedrops containing an anesthetic.

  Using the slit lamp, your doctor moves the tonometer to touch your cornea and determine the eye pressure. Because your eye is numbed, the test doesn't hurt.

• Noncontact tonometry. This method uses a puff of air to estimate the pressure in your eye. No instruments touch your eye, so you won't need an anesthetic. You'll feel a momentary pulse of air on your eye, which can be startling.

If your eye pressure is higher than average or your optic nerve looks unusual, your doctor might use a pachymeter, which uses sound waves to measure the thickness of your cornea. The most common way of measuring corneal thickness is to put an anesthetic drop in your eye, then place a small probe in contact with the front surface of the eye. The measurement takes seconds.

You might need more-specialized tests, depending on your age, medical history and risk of developing eye disease.

Results from an eye exam include:

• Whether you need vision correction, either through glasses, contact lenses or surgery
• Whether your eyes are healthy, or you have cataracts, glaucoma or retinal disorders, such as macular degeneration or diabetic retinopathy

If you need corrective lenses, your doctor will give you a prescription. If your eye exam yields other abnormal results, your doctor will discuss with you the next steps for further testing or for treating an underlying condition.