What means diopter?

Scarcely any other term is used by the optician as often as dioptry. But apart from the opticiens, few can explain it.

But it is not that hard: Nearsighted people see things in the distance worse than objects nearby. This is because the eye lens does not image distant objects exactly on the retina, but farther. In the case of the far-sighted ones, the lens concentrates the light too little. Dioptry is now the measure for the strength with which a spectacle lens breaks the light so that the objects are reproduced exactly on the retina and are thus sharp.

At the same time, the diopter is also the index for the defective vision of the eye. Minus values correspond to myopia, plus values of hyperopia. Whether positive or negative: the higher the diopter count, the stronger the refractive power of the spectacle lens and thus the defective vision.

For example: A myopic person without his glasses sees to a maximum of one meter, his or her prescription is - 1.00 of a diopter to be able to see the distance. Seeing as far as up to 50 centimeters means already a prescription of -2.00 diopters, seeing sharp up to 33 centimeters a prescription of -3.00 of a diopter is necessary to see the distance and so on.