A complete eye exam involves a series of tests designed to evaluate your vision and check for eye diseases. Your doctor may use odd-looking instruments, aim bright lights directly at your eyes and request that you look through a seemingly endless array of lenses. Each test during an eye exam evaluates a different aspect of your vision.

When to have an eye exam

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

• Children 5 years and younger. For children under 3, your pediatrician will likely look for the most common eye problems — lazy eye, crossed eyes or turned-out eyes. Depending on your child's willingness to cooperate, his or his first more comprehensive eye exam should be done between the ages of 3 and 5.

• School-age children and adolescents. Have your child's vision checked before he or she enters first grade. If your child has no symptoms of vision problems and you don't have a family history of vision problems, have your child's vision rechecked every two years. If your child does have vision problems or a family history of vision problems, have your child's vision rechecked as advised by your eye doctor.

• Adults. In general, if you're healthy and have no symptoms of vision problems, you should have your vision checked once in your 20s and twice in your 30s. Between ages 40 and 65, have your vision checked every two to four years. After age 65, get your eyes checked every one to two years. If you wear glasses, have a family history of eye disease or have a chronic disease — such as diabetes — that puts you at greater risk of eye disease, you need to have your eyes checked more frequently. You might also need more frequent eye exams to check for retinal problems if you were born prematurely or to monitor your eyes for glaucoma if you're of African-American heritage.

Three kinds of eye specialists may perform an eye exam:

• Ophthalmologists. Ophthalmologists are medical doctors who provide full eye care, such as giving you a complete eye exam, prescribing corrective lenses, diagnosing and treating complex eye diseases, and performing eye surgery.

• Optometrists. Optometrists provide many of the same services as ophthalmologists, such as evaluating your vision, prescribing corrective lenses, diagnosing common eye disorders and treating selected eye diseases with drugs. But you'll likely be referred to an ophthalmologist for more complex eye problems and for conditions requiring surgery.

• Opticians. Opticians fill prescriptions for eyeglasses, including assembling, fitting and selling them. Some opticians also sell and fit contact lenses.