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The location of the eyes enables us to see length, width, depth, and distance of an object. The eye has three layers: the sclera, choroid, and retina.

The sclera is the outer white layer that maintains the shape of the eye. Muscles attached to the sclera control eye movements. Choroid is the middle layer that contains the blood vessels. The cornea is a clear circular area in the sclera where light enters the eye. The pupil is the circular opening in the front of the choroid. The iris is the colored smooth muscle surrounding the pupil, which adjusts the size of the opening according to the brightness of light.

The lens is located behind the pupil and between the anterior and posterior chambers. The lens is a transparent flexible biconvex structure that bends or refracts light rays so they focus on the nerve cells of the retina. The chambers are filled with a watery fluid that gives shape to the eye and helps refract the light rays. The anterior fluid is called the aqueous humor and the posterior fluid is called the vitreous humor. The retina is the inner layer and contains the nerve cells; the rods and cones; and the bipolar cells. Rods are sensitive to light but do not sense color. Cones sense color. The highest concentration of cones is in the fovea centralis. The rods and cones synapse with bipolar cells, which then synapse with the ganglia cells whose axons form the optic nerve. Light rays enter the eye through the cornea, pupil, and lens; where the light rays are bent and refracted to focus them on the rods and cones which transmit the stimulus to the optic nerve and then to the occipital lobe of the brain for interpretation.