Let us understand how the human eye helps us in seeing objects. The eye is roughly spherical in shape.

• Cornea: Light mainly falls on the cornea, the white clear front part of the eye which is slightly bulging forward. It is tough and protects the interior of the eye from accidents.
• Iris: The iris(a muscular structure behind the cornea) of the eye controls the amount of light reaching the interior of the eye by automatically adjusting the size of the pupil. The iris is that part of the eye which gives it the colour such as black, brown, green eyes commonly called cat-eyes etc
• Pupil: The pupil regulates and controls the amount of light entering the eye.
• Lens: The eyes crystalline biconvex shaped lens is located behind the pupil. It further focuses the light on the retina.
• Ciliary Muscles: The lens is contracted and relaxed by the ciliary muscles. The focal length is varied by this movement.
• Retina: The lens forms an inverted real image of the object on the retina. The retina contains several nerve cells which convert the optical images to signals to the brain via the optic nerve.
• Nerve Cells: There are 2 types of nerve cells. (i) Cones : which are sensitive to bright light and help us recognize color (ii) Rods: which are sensitive to dim light.
• Brain: The brain again inverts the image, decodes this signal and then we see the image.