Optical power (dioptric power or refractive power) is the degree to which a lens or mirror converges or diverges light. A lens is an optical device with perfect or approximate Axial symmetry which transmits and refracts Light, converging or diverging A mirror is an object with a surface that has good Specular reflection; that is it is smooth enough to form an Image. It is equal to the reciprocal of the focal length of the device. The focal length of an optical system is a measure of how strongly it converges (focuses or diverges (diffuses Light. The dioptre is the most common unit of measurement of optical power. A dioptre, or diopter, is a Unit of measurement of the Optical power of a lens or curved Mirror, which is equal to the reciprocal The SI unit for optical power is the inverse metre (m^-1).

For two or more thin lenses in contact, the optical power of the combined lenses is very well approximated by the sum of the individual optical powers of each lens. In Optics, a thin lens is a lens with a thickness (distance along the Optical axis between the two surfaces of the lens that is negligible compared Optical powers are commonly used to characterize lenses used in ophthalmology and for geometric ray tracing. Ophthalmology is the branch of Medicine which deals with the diseases and surgery of the visual pathways including the Eye, Brain In physics ray tracing is a method for calculating the path of Waves or Particles through a system with regions of varying propagation Velocity, absorption

An eye that has too much or too little refractive power to focus light onto the retina has a refractive error. Eyes are organs that detect Light, and send signals along the Optic nerve to the visual areas of the brain In Geometrical optics, a focus, also called an image point, is the point where Light rays originating from a point on the object converge. The vertebrate retina is a light sensitive part inside the inner layer of the Eye. A refractive error, or refraction error, is an error in the focusing of Light by the Eye and a frequent reason for reduced Visual acuity A myopic eye has too much power so light is focused in front of the retina (e. Myopia (from Greek: μυωπία myopia "near-sightedness" also called near- or short-sightedness, is a refractive defect g. , the focal length of the lens is too short). The lens is a transparent biconvex structure in the Eye that along with the Cornea, helps to Refract Light to be focused Conversely, a hyperopic eye has too little power so when the eye is relaxed, light is focused behind the retina (e. Hyperopia, also known as farsightedness or longsightedness, is a Defect of vision caused by an imperfection in the Eye (often when g. , the lens's focal length is too long). An eye with a refractive power in one meridian that is different from the refractive power of the other meridians has astigmatism. This article is about the Perimetry concept For other uses of the word see Meridian. Astigmatism is an optical defect whereby vision is blurred due to the inability of the optics of the eye to focus a point object into a sharp focused image on the retina Anisometropia is the condition in which one eye has a different refractive power than the other eye. Anisometropia is the condition in which the two Eyes have unequal Refractive power; that is are in different states of Myopia (nearsightedness Hyperopia

See also

• Vergence