Health Library

Our Health Library information does not replace the advice of a doctor. Please be advised that this information is made available to assist our patients to learn more about their health. Our providers may not see and/or treat all topics found herein.

Diopter

The diopter is a unit of measurement used to describe how well a person sees.

Farsightedness is measured in positive diopters, and nearsightedness is measured in negative diopters. Astigmatism is measured in diopters that can be either positive or negative.

With diopters, the farther a measurement is from 0, the more severe the refractive error. For example, if a person has -4 diopters of nearsightedness, it means that the farthest point you can see clearly is one-fourth of a meter (about 10 inches) from your eye.