Optical power or dioptric power or refractive power is the degree to which a lens or mirror converges or diverges light. It is equal to the reciprocal of the focal length of the device. The dioptre is the unit of measurement of optical power. A lens. ... A mirror is a surface with good specular reflection that is smooth enough to form an image. ... The focal point F and focal length f of a positive lens, a negative lens, a concave mirror, and a convex mirror. ... A dioptre (also diopter) is a unit of curvature equal to one per metre; that is, inverse metres, or 1/(metres). ...

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. Optical powers are commonly used to characterize lenses used in ophthalmology and for geometric ray tracing. An optical refractor in use. ... A ray traced scene. ...

An eye that has too much or too little refractive power to focus light onto the retina has a refractive error. A myopic eye has too much power so light is focused in front of the retina (e.g. the focal length of the lens is too short). Conversely, a hyperopic eye has too little power so when the eye is relaxed, light is focused behind the retina (e.g. the lens' focal length is too long). An eye with a refractive power in one meridian that is different than the refractive power of the other meridians has astigmatism. Anisometropia is the condition in which one eye has a different refractive power than the other eye. This article refers to the sight organ. ... The focus or image point is the point where light rays, originating from a point in the object, converge [1]. The principal focus or focal point of a lens or parabolic mirror is the point onto which collimated light parallel to the axis is focused. ... Human eye cross-sectional view. ... Refraction error is an error in the focussing of light by the human eye. ... Normal vision for a achromatopsic colour-blind person. ... The lens or crystalline lens is a component of the eye. ... Astigmatism is a refraction error of the eye in which there is a difference in degree of refraction in different meridians. ... Anisometropia is a condition in which the lenses of the two eyes have different focal lengths; that is, are in different states of myopia (nearsightedness) and hyperopia (farsightedness). ...