Definition of a Vision Test

Vision is a complex process involving gathering visual information, processing that information, then responding to it with appropriate decisions or movements. There are tests to measure each aspect of a person's vision. Optometrists and other eye doctors always start with a routine eye exam to check ocular health and visual acuities. If other tests are indicated, they are usually scheduled for another time.

Ocular health

• Doctors perform vision tests to check the health of the eyes at every regular eye exam. They look at the physical appearance of the eyes to make sure there are no visible symptoms of any problems. They also do ophthalmoscopy, looking at the optic nerve through an instrument called an ophthalmoscope, which magnifies the inside of the eye. If they find any abnormalities, they will follow up with more detailed testing. For instance, if the optic nerve looks unusual, the doctor may test an older patient to rule out glaucoma.

Snellen Eye Chart

• The vision test to measure a person's visual acuities starts with the Snellen Eye Chart. The chart is made up of a series of black letters on a white background displayed in rows. The largest letters are on top, and the smallest letters are on the bottom, although modern optometry offices also have a computer version of the chart that allows a doctor to display one letter in isolation. This chart is used to measure a person's distance vision and the expected measurement, 20/20, is considered normal. People who cannot clearly see the letters that a normal eye can discern at 20 feet may need glasses.

Phoroptor Tests

• The phoroptor is the standard instrument used to measure refraction. If a person does not have 20/20 vision, the phoroptor will help the eye doctor determine what corrective lenses to prescribe. The doctor will experiment with different combinations of lenses and ask patients for feedback about which gives them the most comfortable and clear vision. The phoroptor also can help the doctor assess phorias, tropisms and astygmatisms. In other words, if the way a patient's eyes are aligned or work together or the shape of the corneas contribute to visual blur, the phoroptor can help the doctor diagnose the problem and decide on which lenses to use in the treatment.

Learning-Related Vision Skills

• Developmental optometrists also test their patients' learning-related vision skills. People who frequently lose their place when reading may do poorly on the Developmental Eye Movement test. People who have difficulty with spelling or geometry, for example, may be referred to a developmental optometrist for an assessment of their visual perceptual development. People who have very poor hand-eye coordination may be given a test of their Visual-Motor Integration skills.

Expert Insight

• The American Optometric Association recommends that everyone receive an annual eye exam. Many optometrists participate in the American Optometric Association's InfantSee program. They give free comprehensive vision examinations to babies. It is a great way to rule out any rare but dangerous ocular cancers and to make sure that your baby's vision is developing normally. In addition, several states require children to receive a comprehensive vision examination before they're admitted to kindergarten. Not only are vision tests important to a person's health; they also can be key to preventing and resolving academic challenges that have a visual component, as is the case for an estimated 20 percent of American students.