A Snellen Chart is a tool used by eye care professionals to measure visual acuity, which is the clarity or sharpness of vision. It typically consists of rows of letters that decrease in size from top to bottom. Patients stand a specific distance away from the chart, usually 20 feet, and read the letters aloud to determine their vision level. The results from a Snellen Chart are expressed as a fraction, such as 20/20, where the first number indicates the distance from the chart and the second number represents the distance at which a person with normal vision can read the same line. This helps identify any vision problems that may require further evaluation or treatment.