By Caity Tarbert, Tests.com Contributing Writer
Vision tests check one’s eyesight, including the ability to see near and far, as well as peripheral vision and color vision. Prevent Blindness America, a volunteer organization that works to encourage eye health and safety, recommends eye examinations at least once every five years for Caucasians and once every four years for African-Americans. Furthermore, visits to an ophthalmologist or optometrist should increase in frequency as one grows older or if one experiences difficulties seeing.
Types of Vision Tests
The most common type of vision test is known as a visual acuity test. It involves reading letters or symbols from an eye chart. The Snellen chart, the most common chart used for testing distance vision, consists of rows of letters that the patient is instructed to read aloud. Seated or standing from a distance of 20 feet away, the patient will cover one eye and read the smallest row of letters he or she can see clearly. Then the health professional will have the patient switch eyes and repeat the process. Finally, the patient will read the smallest row of letters he or she can see with both eyes open. The near test is very similar to the Snellen test, but the patient will hold a card with varying sizes of print on it at a distance of about 14 inches from his face. He will then be asked to read the paragraph containing the smallest print that can be comfortably read. Each eye is tested separately, and then both eyes are tested together.
A visual field test is used by health professionals to check peripheral vision. The most common visual field test is known as the confrontation test. In this test, the vision screener will stand a few feet away from the patient and instruct her to cover one eye and gaze at the screener's nose. The screener will then move his finger through the patient's visual field and ask her to signal when she sees the finger.
Another aspect of vision testing is a color vision test to check for any degree of color blindness. The patient is typically shown a picture with an array of dots in various colors and asked to identify a different-colored number or symbol that is hidden amongst the other dots.
How Vision Tests Work
The eye is a complex organ, and the ability to see clearly is an essential part of the five senses. When light is reflected from an object through the cornea, it moves through the lens and then reaches the retina at the very back of the eye. There it meets a layer of cells called rods and cones, which are responsible for color vision. Visual information travels from the retina to the brain via the optic nerve in order to allow individuals to interpret the images they see. Vision tests work by examining the various parts of the eye and determining whether or not they are functioning properly. For example, if an image is not focused properly when it moves through the lens, an individual may have visual acuity problems. If there are issues with a person's rods and cones, they may have color blindness. There are no risks associated with vision screenings.
Vision Test Results
The results of visual acuity tests are reported in the form of a fraction. 20/20 is known as perfect vision. On an eye chart, each line is assigned a fraction that represents visual acuity. The numerator of the fraction is the distance the patient is from the eye chart. The denominator represents the distance an eye with normal vision can read the same line. A person with 20/30 vision can interpret their results as follows – They are 20 feet away from the eye chart, and they are able to read a line of print that a normal eye could read at 30 feet away. Therefore, they may need corrective lenses in order to bring their vision back to 20/20. A person with 20/16 vision has better-than-average vision.
Preparation for Testing
To prepare for an eye exam, candidates should write down a list of any vision problems or difficulties experienced and should be familiar with the family vision history. Candidates should also bring glasses and contact lenses, if they wear them, as well as a health insurance card from a vision plan.
Have you had problems with your eyesight, or would you like to schedule a routine vision test? Please consult our Vision Test Directory to locate a health professional in your area.
Sources: Prevent Blindness America, preventblindness.org/vic; WebMD, webmd.com
