8.2 Eye and Ear Basic Concepts
Open Resources for Nursing (Open RN)
Anatomy of the Eye
Our sense of vision occurs due to transduction of light stimuli received through the eyes. The eyes are located within either orbit in the skull. See Figure 8.1[1] for an illustration of the eye. The eyelids, with lashes at their leading edges, help to protect the eye from abrasions by blocking particles that may land on the surface of the eye. The inner surface of each lid is a thin membrane known as the conjunctiva. The conjunctiva extends over the white areas of the eye called the sclera, connecting the eyelids to the eyeball. The iris is the colored part of the eye. The iris is a smooth muscle that opens and closes the pupil, the hole at the center of the eye that allows light to enter. The iris constricts the pupil in response to bright light and dilates the pupil in response to dim light. The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. The cornea, with the anterior chamber and lens, refracts light and contributes to vision. The cornea can be reshaped by surgical procedures such as LASIK. The innermost layer of the eye is the retina that contains the nervous tissue and specialized cells called photoreceptors for the initial processing of visual stimuli. Two types of photoreceptors within the retina are the rods and the cones. The cones are sensitive to different wavelengths of light and provide color vision. Tears are produced by the lacrimal gland that is located beneath the lateral edges of the nose. Tears flow through the lacrimal duct to the medial corner of the eye and flow over the conjunctiva to wash away foreign particles. Movement of the eye within the orbit occurs by the contraction of six extraocular muscles that originate from the bones of the orbit and insert into the surface of the eyeball. The extraocular muscles are innervated by the abducens nerve, the trochlear nerve, and the oculomotor nerve (cranial nerves III, IV, and V).[3] See the illustration of the extraocular muscles in Figure 8.2.[4]
Video Review for Anatomy of the Eye[5]
Common Disorders of the Eye
Eye disorders that nurses commonly see in practice include myopia, presbyopia, color blindness, dry eye, conjunctivitis, styes, cataracts, macular degeneration, and glaucoma.
Myopia
Myopia is impaired vision, also known as nearsightedness that makes far-away objects look blurry. It happens when the eyeball grows too long from front to back or when there are problems with the shape of the cornea or the lens. These problems make light focus in front of the retina, instead of on it, causing blurriness. See Figure 8.3[6] for a simulated image of a person’s vision with myopia. Nearsightedness usually becomes apparent between ages 6 and 14. It is corrected with glasses, contacts, or LASIK surgery.[7]
Presbyopia
Presbyopia is impaired near vision. It commonly occurs in middle-aged and older adults, making it difficult to clearly see obje