How Do You Use an Eye Chart to Test Vision?

How Do You Use an Eye Chart to Test Vision?

How Do You Use an Eye Chart to Test Vision?

Health care professionals test visual acuity by evaluating how well a patient can see letters on a chart from different distances, states Healthline. The Snellen test is one common format that involves reading rows of letters or symbols of various sizes from a chart positioned 14 to 20 feet away.

Visual acuity tests determine the level of detail patients perceive when looking straight ahead, and they are usually performed as part of a routine eye exam, explains MedlinePlus. One method requires instructing the patient to cover one eye with a hand or paddle while identifying the letters on a standardized chart. As the letters become progressively smaller, health care professionals measure the point where the patient is unable to read the letters at the current distance.

A score of 20/20 is considered normal because the patient stood 20 feet from the chart and accurately perceived the amount of detail expected at this distance, according to the American Optometric Association. In contrast, a person with a 20/40 score must stand within 20 feet of the chart to read at an accuracy level considered normal for someone standing 40 feet away. Visual acuity tests do not provide a definitive measurement of vision, and they are typically performed along with examinations that test peripheral vision, depth perception, eye coordination and other skills.