eye
(ī 
)
The organ of vision.
SEE: illus.
Anatomy: The eyeball has three layers: the inner retina, which contains the photoreceptors; the middle uvea, which contains the choroid, ciliary body, and iris; and the outer sclera, which includes the transparent cornea. The eyeball contains two cavities: the anterior cavity and the posterior cavity. The smaller anterior cavity is in front of the lens and is further divided by the iris into an anterior chamber, filled with aqueous humor, and a posterior chamber, filled with the vitreous. Behind the lens is the larger posterior cavity, which contains the vitreous. The lens is behind the iris, held in place by the ciliary body and suspensory ligaments called zonules. The visible portion of the sclera is covered by the conjunctiva. Six extrinsic muscles move the eyeball: the superior, inferior, medial, and lateral rectus muscles, and the superior and inferior oblique muscles.
Nerve supply: The optic (second cranial) nerve contains the fibers from the retina. The eye muscles are supplied by the oculomotor, trochlear, and abducens (third, fourth, and sixth cranial) nerves. The lid muscles are supplied by the facial nerve to the orbicularis oculi and the oculomotor nerve to the levator palpebrae. Sensory fibers to the orbit are furnished by ophthalmic and maxillary fibers of the fifth cranial (trigeminal) nerve. Sympathetic postganglionic fibers originate in the carotid plexus, their cell bodies lying in the superior cervical ganglion. They supply the dilator muscle of the iris. Parasympathetic fibers from the ciliary ganglion pass to the lacrimal gland , ciliary muscle, and constrictor muscles of the iris.
Physiology: Light entering the eye passes through the cornea, then through the pupil, and on through the crystalline lens and the vitreous to the retina. The cornea, aqueous humor, lens, and vitreous are the refracting media of the eye. Changes in the curvature of the lens are brought about by its elasticity and by contraction of the ciliary muscle. These changes focus light rays on the retina, thereby stimulating the rods and cones. The rods detect light, and the cones detect colors in the visible spectrum. The visual area of the cerebral cortex, located in the occipital lobe, registers them as visual sensations. The amount of light entering the eye is regulated by the iris; its constrictor and dilator muscles change the size of the pupil in response to varying amounts of light. The eye can distinguish nearly 8 million differences in color. As the eye ages, objects appear greener. The principal aspects of vision are color sense, light sense, movement, and form sense.
Patient Care: When injury to the eye occurs, visual acuity is assessed immediately. If the globe has been penetrated, a suitable eye shield, not an eye patch, is applied. A penetrating foreign body should not be removed. All medications, esp. corticosteroids, are withheld until the patient has been seen by an ophthalmologist.
The patient is assessed for pain and tenderness, redness and discharge, itching, photophobia, increased tearing, blinking, and visual blurring. When any prescribed topical eye medications (drops, ointments, or solutions) are administered, the health care provider should wash his or her hand s thoroughly before administering the agent. The patient's head is turned slightly toward the affected eye; his or her cooperation is necessary to keep the eye wide open. Drops are instilled in the conjunctival sac (not on the orb), and pressure is applied to the lacrimal apparatus in the inner canthus if it is necessary to prevent systemic absorption. Ointments are applied along the palpebral border from the inner to the outer canthus, and solutions are instilled from the inner to the outer canthus. Touching the dropper or tip of the medication container to the eye should be avoided, and hand s should be washed immediately after the procedure.
Both patient and family are taught correct methods for instilling prescribed medications. Patients with visual defects are protected from injury, and family members are taught safety measures. Patients with insufficient tearing or the inability to blink or close their eyes are protected from corneal injury by applying artificial tears and by gently patching the eyes closed. The importance of periodic eye examinations is emphasized. Persons at risk should protect their eyes from trauma by wearing safety goggles when working with or near dangerous tools or substances. Tinted lenses should be worn to protect the eyes from excessive exposure to bright light. Patients should avoid rubbing their eyes to prevent irritation or possibly infection.
SEE: eyedrops; artificial tears.
Corticosteroids should not be administered topically or systemically until the patient has been seen by a physician, preferably an ophthalmologist.aphakic e.An eye from which the crystalline lens has been removed.
artificial e.A prosthesis for placement in the orbit of an person whose eye has been removed. SYN: false eye; glass eye; ocular prosthesis.
SEE: ocularist.
black e.Bruising, discoloration, and swelling of the eyelid and tissue around the eye due to trauma.
Application of ice packs during the first 24 hr will inhibit swelling. Hot compresses after the first day may aid absorption of the fluids that produce discoloration.
ABBR: CLARE
Ocular irritation in a contact lens wearer, as from bacterial infection or an allergic reaction to a contaminant absorbed or entrapped by the lens.SEE: cross-eye.
dark-adapted e.An eye that has become adjusted for viewing objects in dim light; one adapted for scotopic, or rod, vision. Dark adaptation depends on the regeneration of rhodopsin, the light-sensitive glycoprotein in the rods of the eye.
dominant e.The eye to which a person unconsciously gives preference as a source of stimuli for visual sensations. The dominant eye is usually used in sighting down a gun or looking through a monocular microscope.
dry e.Insufficient quantity and /or quality of tears caused by aging, the environment, hormonal changes, or disease. This condition produces pain and discomfort in the eyes. Dry eye may occur in any disorder that scars the cornea (such as erythema multiforme), Sjögren syndrome, lagophthalmos, Riley-Day syndrome, absence of one or both of the lacrimal gland s, paralysis of the facial or trigeminal nerves, medication with atropine, and deep anesthesia. Suitably prepared water-soluble polymers are effective in treating this condition. SYN: alacrima.
SEE: Sjögren syndrome.
exciting e.In sympathetic ophthalmia, the damaged eye, the source of sympathogenic influences.
fixating e.In strabismus, the eye directed toward the object of vision.
SEE: Klieg eye.
light-adapted e.An eye that has become adjusted to viewing objects in bright light; one adapted for phototic (cone) vision. In this type of eye, most rhodopsin has broken down.
raccoon e.Bruising surrounding the eyes. After trauma this finding suggests basilar skull fracture. SYN: pand a eye.
squinting e.An eye that deviates from the object of fixation in strabismus.
sympathizing e.In sympathetic ophthalmia, the uninjured eye, which reacts to the pathological process in the injured eye.