Types of Eye Tests

During an eye exam, an ophthalmologist, or eye doctor, checks for eye diseases that could lead to vision loss if untreated. There are several types of eye tests that can be performed to detect the presence of eye problems. These include nearsightedness, glaucoma and color blindness. When not diagnosed or properly treated, these conditions can result in eyestrain, headaches and blurred vision or vision loss.

Visual Acuity Test

• The visual acuity test is one that many people associate with having an eye exam. In a visual acuity test, the person stands about 20 feet away from an eye chart, which contains letters of various sizes. If the person wears glasses or contacts, they are removed for the exam. One eye is covered and the person is asked to read the smallest line of letters possible. Visual acuity testing is done when there is a change or problem with vision. The results of a visual acuity test are written as a fraction. Normal vision is 20/20, with the top number representing the distance the person is standing from the chart during the test and the bottom number indicating the distance at which a person with normal vision can read the line of letters. An abnormal result on a visual acuity test could point to the presence of conditions like farsightedness, nearsightedness or astigmatism, which can be treated with corrective lenses or surgery.

Visual Field Test

• A visual field test is performed by a doctor to screen for glaucoma. Glaucoma is a condition in which the pressure in the eye, known as intraocular pressure, rises to unhealthy levels. When detected early, glaucoma can be treated with medication or surgery, thus preventing vision loss. The visual field test is the part of a glaucoma screening that helps an eye doctor measure a person's level of peripheral, or side, vision. During a visual field test, the person presses a button to indicate that he recognizes a flash of light directed to the sides, top or bottom of his eyes while he is looking straight ahead. The test can be completed in as little as three minutes. In those who have already been diagnosed with glaucoma, the visual field test shows if the condition is stable or worsening.

Color Vision Test

• The color vision test is used to determine if a person is able to distinguish between different colors. During a color vision test, the person is seated and is shown symbols of colored dot patterns. The patterns are on a background of random colors and the person is asked to identify the symbols with one eye covered. The test plates are held 14 inches from the person's face. This test may be performed on a child or an adult, and glasses may be worn during the color vision test. The color vision test may indicate problems affecting the optic nerve, which is the main nerve that connects the eye to the brain. Complete color blindness, or achromatopsia, is diagnosed when a person can see only shades of gray. Other color vision problems include difficulty in determining the difference between blue/green and red/green (protanopia) or red/purple and green/purple (deuteranopia). Prevent Blindness America notes that there is no cure for color vision deficiencies. However, some people with these conditions can distinguish colors based on brightness, and special glasses can help the wearer to identify certain colors.