Dioptre

Diopter (Greek: means for vision) is the unit of measurement for power ( rarely also: refractive index ) optical systems and represents the reciprocal of the length unit meters. Your unit mark in Germany is dpt.

Legal Status

The unit diopter is used as a legal entity in the countries of EU and Switzerland in the indication of the power of optical systems, especially in ophthalmic optics. The optical system may be an optical lens, a curved mirror or an eye.

For the diopter no international unit symbol is fixed. The character " dpt " is listed in the German unification Regulation, but does not appear in the underlying Directive 80/181/EEC.

Human Eye

At the suggestion of the French ophthalmologist Ferdinand Monoyer the diopter 1872 introduced in the ophthalmic optics. The refractive power of the emmetropic human eye is healthy in akkommodationslosem state about 59-60 diopters (equivalent to a focal length of about 16.6 mm) and can be extended to adapt to smaller viewing distances; this adaptability is age-dependent and can be from about the age of 25 after.

Converging lenses are used to correct hyperopia, diverging lenses, the correction of myopia and astigmatism toric lenses to correct a. The power is also the characteristic size of a lens or an eyepiece with diopter compensation. The larger it is, the stronger the correction of refractive errors.

To estimate the strength of a required reading glasses in presbyopia following rule of thumb is:

Example: Reading distance 1/3 m ≙ 3.0 D; minimum visual distance: 1/ 2 m ≙ 2.0 D; ( a converging lens so ) 2.0 dpt = 1.0 D required - that is a pair of reading glasses from 3.0 dpt.