Eye Anatomy

The eye is a sensory organ that reacts to light.  It allows for the conscious perception of light, differentiation of color, and depth perception through stereoscopic vision (the use of both eyes to produce one coherent three-dimensional image).  In the image below,  we describe some basic anatomy.   

The sclera is the white, opaque part of the eye that encloses most of the eyeball and is surrounded by the conjunctiva, a thin mucous membrane that covers its outer surface everywhere except on the cornea.  the cornea is the clear outermost part of the eye through which light enters.  If we compare the eye to a camera, the sclera would be the camera's outer shell and the cornea would be the outer lens.  The cornea does most of the focusing for objects at distance.  Beneath the cornea is the iris, which gives color to our eyes, and the pupil, and aperture through which light enters the eye proper.  Light is brought into sharp focus by the natural, crystaline lens.  A muscle surrounding the lens can squeeze it to make it more convex  and increase its focusing power so that we may  focus on nearby objects or read.  The clear gelatinous mass that fills the inside of the eye to provide structural support is the vitreous.  The retina is a membrane that lines the rear of the globe and converts visual signals into electrical impulses.  In our analogy, the retina is like the film of a camera.  The cornea and the lens bring light into sharp focus on the macula, a specific region of the retina.  Rod and cone cells, photoreceptor cells on the retina, sense actual photons (particles of light) and differentiate their frequencies which we interpret as the various colors.  This information travels along the optic nerve and on to the brain's visual cortex.  We have limited knowledge of how visual signals are processed, and in particular, of how the brain copes with the limited "channel capacity" of the optic nerve.  Research to provide a more thorough understanding of how our minds produce a detailed, continuous image is ongoing.

Six orbital muscles outside of the eye control movement.  Four are responsible for movement  up, down and sideways, and the other two keep the eyes aligned as the head moves.  the eyelids, the thin folds of skin which cover and protect the eyes from debris and perspiration, are also responsible for spreading secretions of the eye and the tear film to lubricate the cornea, which must always be kept moist.