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.

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.

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.