Vision tests check many different functions of the eye. The tests measure your ability to see details at near and far distances, check for gaps or defects in your field of vision, and evaluate your ability to see different colors.

• Visual acuity tests are the most common tests used to evaluate eyesight. They measure the eye's ability to see details at near and far distances. The tests usually involve reading letters or looking at symbols of different sizes on an eye chart. Usually, each eye is tested individually and then both eyes are tested together with and without corrective lenses (if you wear them). Several types of visual acuity tests may be used.
• Refraction is a test that measures the eyes' need for corrective lenses (refractive error). It is usually done after a visual acuity test. Refractive errors, such as nearsightedness or farsightedness, occur when light rays entering the eye do not focus exactly on the nerve layer (retina) at the back of the eye. This causes blurred vision. Refraction is done as a routine part of an eye examination for people who already wear glasses or contact lenses, but it will also be done if the results of the other visual acuity tests show that your eyesight is below normal and can be corrected by glasses.
• Visual field tests are used to check for gaps in your side (peripheral) vision. Your complete visual field is the entire area seen when your gaze is fixed in one direction. The complete visual field is seen by both eyes at the same time, and it includes the central visual field-which detects the highest degree of detail-and the peripheral visual fields.
• Color vision tests check your ability to distinguish colors. It is used to screen for color blindness in people with suspected retinal or optic nerve disease or who have a family history of color blindness. The color vision test is also used to screen applicants for jobs in fields where color perception is essential, such as law enforcement, the military, or electronics. Color vision tests only detect a problem; further testing is needed to identify what is causing the problem.

Why It Is Done

Visual acuity tests may be done:

• As part of a routine eye exam to screen for vision problems. How often you should have routine eye exams changes as you age:
  • Once between the ages of 3 and 5
  • Before a child begins first grade, then every 2 years
  • Once between the ages of 20 and 29
  • Twice between the ages of 30 and 39
  • Every 2 to 4 years between the ages of 40 and 65
  • Every 1 to 2 years after age 65
• To monitor an eye problem, such as diabetic retinopathy.
• To determine if you need glasses or contact lenses to improve your vision.
• After an injury to the eye.
• When you obtain or renew your driver's license or for some types of employment.