In general, visual acuity tests show that the vision is 1.5, 0.2, or 0.1. However, if you wear contact lenses, you have probably heard of prescribed lenses with -0.75D, -3.00D, etc. How are the lens diopter different from vision?
The visual acuity is a subjective figure that determines how are you can see while diopter is an objective measurement of refracting power. This means that diopters can be completely different depending on the health of your eyes even though the results of visual acuity are the same.
Diopter is represented by D and refers to the reciprocal of the focal length (m, in meters). In other words, -1.00D means a lens with a focal length of 1m, and -4.00D means a lens with a focal length of 25cm (1/4m). The concave lens required for myopic correction is indicated by (-), the convex lens required for the hyperopia correction is represented by (+). The larger the number (farther from zero) means it will be more myopic or hyperopic.