dioptri

Dioptri is a unit of measurement used to express the refractive power of a lens or optical system. It is defined as the reciprocal of the focal length in meters. For example, a lens with a focal length of 0.5 meters has a refractive power of 1 / 0.5 = 2 dioptri. Conversely, a lens with a focal length of -0.25 meters has a power of 1 / -0.25 = -4 dioptri. Positive dioptri values indicate a converging lens, which brings parallel light rays together at a focal point. Negative dioptri values indicate a diverging lens, which spreads parallel light rays apart.

The concept of dioptri is fundamental in optics, particularly in the field of optometry and ophthalmology. Eyeglass prescriptions are given in dioptri to correct refractive errors such as myopia (nearsightedness) and hyperopia (farsightedness). Myopia is typically corrected with negative dioptri lenses, while hyperopia is corrected with positive dioptri lenses. Astigmatism, an irregular curvature of the cornea or lens, is also measured and corrected using dioptri, often requiring different power corrections in different meridians of the eye. The diopter system allows for a standardized and precise way to prescribe and manufacture corrective lenses.