The human eye is a complex optical system made up of various transparent media in addition to a physiological system with numerous components.
The whole ensemble that makes up human vision is called the eyeball. Light strikes the cornea and converges to the retina, forming the images.
For this imaging several physiological phenomena happen. However, for the study of optics we can consider the eye as a convergent lens with variable focal length, being represented as follows:
Such a representation is called reduced eye, and represents the distance between the cornea and the lens and between the lens and the retina, the latter being the distance of the image produced from the lens (P').