What does diopter -3.25 mean?

If parallel light passes through the refractive stroma of the eyeball or light passes through the lens to form a focus at 1 m, the diopter of the refractive stroma or lens is defined as 1 diopter. The diopter is inversely proportional to the focal length, and the shorter the focal length, the greater the diopter. The diopter is represented by D, and the focal length is represented by F (in meters). The relationship between them is as follows:: d =1/f.

For example, the focal length of the lens is 0.5m, and D= 1/0.5=2, that is, the diopter of the lens is 2 diopters. However, people are used to saying 1 .00 diopter as "100 degree".

Therefore, 3.25 diopters is usually called 325 degrees.