The human eye enables us to see the objects around us. It works on the phenomena of refraction of light through a natural convex lens made of transparent living material (tissue) and it enables us to visualise all around us. Human Eye:- The human eye is has the following main parts :- * Cornea : It is the transparent spherical membrane covering the front of the eye. Light enters the eye through this membrane. Most of the refraction of the light rays entering the eye occurs at the outer surface of cornea. * Crystalline lens:- The eye lens is a convex lens made of a transparent, soft and flexible material like a jelly made of proteins. * Iris:- It is a dark muscular diaphragm between the cornea and the lens. It controls the size of the pupil. It is the colour of the iris that we call as the colour of the eye. * Pupil:- It is a small hole between the iris through which light enters the eye. In din light, it opens up completely due to expansion of iris ...