A visual acuity chart is a tool used by eye doctors and optometrists to measure a person's ability to see fine details at

a certain distance. It usually consists of rows of letters or symbols of various sizes that gradually decrease in size

from top to bottom. The person being tested covers one eye and reads the symbols from top to bottom until they

reach a line they cannot read, then their other eye is tested. The results are recorded in a measurement known as

Snellen fractions, which represents the distance at which the symbols can be seen clearly by a person with normal

vision. The standard chart used in most clinics and hospitals is the Snellen chart.