Anatomy of the Human Eye
Picture courtesy of The Physics Classroom Tutorial
The human eye is a hollow ball, filled with fluids called humors that act to hold the shape of the eye. The front of the eye is covered by a transparent membrane called the cornea. The purpose of the cornea is to protect the eye while allowing light to enter. Light is defracted by the cornea before it passes through the pupil. The pupil, or the black part of the eye, is merely an opening for light to pass through. The size of the pupil determines the amount of light allowed to enter the eye. This is controlled by the iris, a pigmented diaphragm that dilates to change the shape of the pupil opening. The light then passes through the crystalline lens. The lens is composed of a fibrous, jelly-like tissue and can change shape to allow the eye to focus on an object. The ciliary muscles control the shape of the lens. The light is focused onto the retina, which is the rod and cone containing surface on the back of the eye. Rods sense intensity of light, and cones sense frequency of light, or color. Rods and cones send these signals to the brain via the optic nerve. This is how we are able to see shapes and colors.