Light rays enter the front of the eye through the transparent cornea. Light passes through the pupil (the dark center of the colored iris) and are focused by the cornea and lens though the vitreous gel onto the retina, much as a camera focuses images onto film. The retina lines the inside of the eye, containing a thin layer of light sensitive cells (rods and cones). The retina translates patterns of light into signals which travel through the optic nerves to the brain, where images are perceived.
The eye is truly like a camera because it not only requires proper focusing but it requires a clear media through which light rays must pass. Any loss of clarity of the structures through which these light rays must pass will interfere with their successful interpretation within the visual cortex of the brain. Examples of disorders which might cause this scattering or absorption of light rays are opacities in the cornea ( corneal scars or abrasions), opacification of the lens (cataract), and cloudiness of the vitreous (by hemorrhage or inflammation.) In addition, the retina itself must be functioning properly to produce a clear, undistorted picture in both the peripheral and central visual fields.