Structure of The Eye

Table 3-1.—Functions of the autonomic nervous system Sympathetic Parasympathetic Dilates pupils. Lessens tonus of ciliary muscles so the eyes may accommodate to see distant objects. Dilates bronchi. Quickens and strengthens the action of the heart. Contracts blood vessels of the skin and viscera so that more blood goes to the skeletal and cardiac muscles where it is needed for “fight or flight.” Relaxes gastrointestinal tract and bladder. Decreases secretions of the gastrointestinal glands. Increases secretion of sweat glands. Causes contraction of sphincters to prevent emptying of bowels or bladder. Constricts pupils. Contracts ciliary muscles so the eyes may accommodate to see objects near at hand. Constricts bronchi. Slows the action of the heart. Dilates blood vessels (except cardiac). Increases contraction of gastrointestinal tract and muscle tone of the bladder. Increases secretions of gastrointestinal glands. No action on sweat glands. Relaxes sphincters so that waste matter can be excreted. ocular muscles, eyelids, conjunctival, and lacrimal apparatus. Structure of The Eye The eye is a hollow ball, or globe, which con- sists of various tissues that perform specific func- tions. The globe, or eyeball, is composed of three layers (fig. 3-45). OUTER LAYER.—The outer layer of the eye is called the sclera. It is the tough, fibrous, pro- tective portion of the globe, commonly called the white of the eye. Anteriorly, the outer layer is transparent and is called the cornea, or the win- dow of the eye. It permits light to enter the globe. The exposed sclera is covered with a mucous mem- brane, the conjunctival, which is a continuation of the inner lining of the eyelids. The lacrimal gland produces tears that constantly wash the front part of the eye and the conjunctival. The tear gland secretions that do not evaporate flow 3-35 Figure 3-45.—Cross section of the eye.