Unit
The concept of the diopter first introduced by the Swedish ophthalmologist Alvar Olympiad shortage. Dioptre (or diopter) is a unit of measurement of the optical power of optical systems. For example, 1 diopter is equal to the optical power of a spherical mirror or an optical lens with a focal length equal to one meter. The optical power in diopters of focal length in meters. The greatest focusing range, which is obtained by using one camera is 200 diopters.
In the definition of a diopter is used, the meter is the unit of SI – the International system of units, but the power in the SI system is not included and is a non-si unit. In the Russian Federation all the power allowed for use equally with the SI units indefinitely. In the international organization of legal Metrology (OIML) DPT refers to the unit that is temporarily introduced until the date set by the national order.
Diopter and sight
The crystalline lens is a biconvex lens. This lens has a variable curvature that provides eye lens ability to accommodate. Accommodation is the ability of the human eye actively multiplying its refractive power by the growth of the optical power of the lens. Thus, by way of accommodation the human eye can only enhance its optical system. In young people the accommodative ability of the ocular optical system is about 14 diopters, this ability gradually decreases to 60-65 years almost lost.
With decreasing ability of the lens to change the curvature, the sharpness of human vision can be improved with the help of external lenses. Such lenses are, for example, glasses or contact lenses. The optical power of the lens that collects the rays, is positive and diffusing the negative. For short-sighted people getting spread lenses for far-sighted, hence the collecting. If a person glasses "plus", then it is diagnosed hyperopia, if the points a "minus" – that the person has myopia.
In fact, the optical power of the lens is designed to fully compensate for the imperfection of the optical power of the lens. And here there is a common misconception that the vision is measured in diopters.