The human eye is one of the most valuable and sensitive sense organs. It enables us to see the wonderful world and the colours around us. On closing the eyes, we can identify objects to some extent by their smell, taste, sound they make or by touch. It is, however to impossible to identify colours while closing the eyes. Thus, of all the sense organs, the human eye is the most significant one as it enables us to see the beautiful, colourful world around us.
- The human eye is like a camera. Its lens system forms an image on a light- sensitive screen called the retina.
- Light enters the eye through a thin membrane called the cornea. It forms the transparent bulge on the front surface of the eyeball.
- The eyeball is approximately spherical in shape with a diameter of about 2.3cm. Most of the refraction for the light rays entering the eye occurs at the outer surface of the cornea. The crystalline lens merely provides the finer adjustment of focal length required to focus objects at different distances on the retina that structure called iris. This structure is situated behind the cornea.
- Iris is a dark muscular diaphragm that controls the size of the pupil. The pupil regulates and controls the amount of light entering the eye. The eye lens forms an inverted real image of the object on the retina.
- The retina is a delicate membrane having enormous number of light- sensitive cells.
- The light-sensitive cells get activated upon illumination and generate electrical signals. These signals are sent to the brain via the optic nerves.