human eye is one of the most valuable and sensitive sense organs.the light is entering to our eye through a thin membrane called CORNEA and falls on a light sensitive screen called RETINA..cornea forms a transparent bulge in front of the eyeball.the eyeball is approximately spherical in shape of diameter 2.3cm.we can find a structure called IRIS behind the cornea.iris is a dark macular diaphragm and controls the amount of light entering the eye.the eye lens forms an inverted real image[as like in a mirror]of the object on the retina. retina is a delicate membrane having enormous no.of light sensitive cells. these light sensitive cells get activated and generate electrical signals. these signals are sent to the brain via the optic nerves the brain then interprets these signals and processes the information that we are seeing the image. These processes takes place quickly and that is why we feels like we se the image at the moment we look at them

It is a natural , complicated optical device ..