Human Eye

 

HUMAN EYE

The interior of the eye is filled with a transparent gel-like substance called the vitreous humor with index of refraction n = 1.337. Light enters in this region through the cornea and lens. Between the cornea and lens is a watery fluid, the aqueous humor with n = 1.336.

human eye

 The iris adjusts automatically to control ten amount of light entering the eye, similar to a camera. The retina, which plays the role of the film or sensor in a camera, is on the curved back surface of the eye. The retina is composed of a many nerves which act to change light energy into electrical signals that travel. Along the nerves to lens of the eye (n= 1.386 to 406) does little of the bending of the light rays.

 most of the refraction is done at the front surface of the cornea at its interface duty air. The lens acts as a fine adjustment for focusing at different distances. This is accomplished by the ciliary muscles, which change the curvature of the lens so that its focal length is changed. To focus on a distant object, the ciliary muscles of the eye are relaxed and the lens is thin. and parallel rays focus at the focal point (on the retina). To focus on a nearby object, the muscles contract, causing the center of the lens to thicken. thus shortening the focal length so that images of nearby objects can be focused on the retina, behind the new focal point. This focusing adjustment is called accommodation.

 The closest distance at which the eye can focus clearly is called the near point of the eye For young adults it is typically 25 cm, as people grow older, the ability to accommodate is reduced and the near point increases