The diopter is a unit of measurement that indicates how much a lens refracts light so that objects are mapped exactly on the retina. Only then we can truly see really sharp. Therefore, a diopter in addition to the power at the same time indicates the strength of our vision. Minus is myopia – values with a positive number of diopters characterize the degree of our farsightedness.
The greater the value of the diopter, the stronger the correction of a visual defect. Where a short-sighted person without glasses sees up to one meter sharp, he needs to correct distance vision with lens with a minus one diopter. When visual acuity to 50 centimeters, the correction is minus two diopters – and only 33 centimeters already minus three diopters.
In a pair of reading glasses with converging lenses the diopter values are in the positive range, because the glasses are slightly curved outward (convex). To read a text at a distance of 35 centimeters pleasantly, normal-sighted people at the age of 45 years usually need a pair of reading glasses at about +0.75 diopters. In free sale you can find glasses with a correction to max. 3.5 diopters (dpt). Filtral provides the following diopters: +1.0; +1.5; +2.0; +2.5; +3.0; +3.5.