Optical power of the lens.

The refractive power of a crystalline lens is determined by surface curvatures, refractive index differences across water-based, vitreous lenses, and the distribution of the refractive index gradient in the lens. Lens power decreases with age, mainly due to a decrease in the contribution of the gradient. Studying the optical properties of a lens (ie, optical power, refractive index distribution, and surface refractive contributions) is difficult due to the position of the lens behind the cornea and pupil, as well as distortions of the rear surface of the lens caused by the lens refractive index gradient.