How is vision measured and what methods are used to assess visual acuity and clarity?

Vision is measured using a standardized eye chart called the Snellen chart, which has rows of letters that decrease in size. Visual acuity, or sharpness of vision, is assessed by determining the smallest line of letters a person can read from a specific distance. Other methods to assess visual clarity include using a visual acuity test, contrast sensitivity test, and visual field test.