Porth's Essentials of Pathophysiology, 4e

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Disorders of Special Sensory Function: Vision, Hearing, and Vestibular Function

C h a p t e r 3 8

The habituation effect is characterized by decreased sensitivity and duration of symptoms. It may occur in as little as 2 weeks or take as long as 6 months. Balance retraining exercises consist of activities directed toward improving individual components of balance that may be abnormal. General conditioning exercises, a vital part of the rehabilitation process, are individualized to the person’s preferences and lifestyle.

her distant vision, a 75-year-old woman is told that she is developing cataracts. A. What types of visual changes occur as the result of a cataract? B. What can the woman do to prevent the cataracts from getting worse? C. What treatment may she eventually need? 3. A 50-year-old woman is told by her eye doctor that her intraocular pressure is slightly elevated and that although there is no evidence of damage to her eyes at this time, she is at risk for developing glaucoma and should have regular eye examinations. A. Describe the physiologic mechanisms involved in the regulation of intraocular pressure. B. Differentiate between open-angle and angle- closure glaucoma in terms of their pathology, manifestations, and treatment. C. See Figure 38-12 to relate the “optic disk cupping” that occurs with glaucoma to the visual field loss that occurs with the disorder. 4. The parents of a newborn infant have been told that their son has congenital cataracts and will require cataract surgery to prevent losing his sight. A. Explain why the infant is at risk for losing his sight if the cataracts are not removed. B. When should this procedure be done to prevent loss of vision? 5. A mother notices that her 13-month-old child is fussy and tugging at his ear and refuses to eat his breakfast. When she takes his temperature, it is 100°F. Although the child attends day care, his mother has kept him home and made an appointment with the child’s pediatrician. In the physician’s office, his temperature is 100.2°F, he is somewhat irritable, and he has a clear nasal drainage. His left tympanic membrane shows normal landmarks and motility on pneumatic otoscopy. His right tympanic membrane is erythematous and there is decreased motility on pneumatic otoscopy. A. What risk factors are present that predispose this child to the development of acute otitis media? B. Are his signs and symptoms typical of otitis media in a child of this age? C. What are the most likely pathogens? What treatment would be indicated? D. Later in the week, the mother notices that the child does not seem to hear as well as he did before developing the infection. Is this a common occurrence, and should the mother be concerned about transient hearing loss in a child of this age?

SUMMARY CONCEPTS

■■ Receptors for the vestibular system that respond to changes in rotational and linear acceleration of the head are located in the fluid-filled semicircular ducts of the inner ear. ■■ The vestibular system has extensive interconnections with neural pathways controlling vision, hearing, balance, and autonomic nervous system function. Signals from the vestibular system initiate head and eye movements to stabilize the visual field and make adjustments in the posture muscles that maintain balance. ■■ Disorders of vestibular function can result from repeated stimulation of the vestibular system such as during car, air, and boat travel (motion sickness); acute infection of the vestibular pathways (acute vestibular neuritis); dislodgement of otoliths that participate in the receptor function of the vestibular system (benign paroxysmal positional vertigo); or distention of the endolymphatic compartment of the inner ear (Ménière disease). R E V I EW E X E R C I S E S 1. The mother of a 3-year-old boy notices that his left eye is red and watering when she picks him up from day care. He keeps rubbing his eye as though it itches. The next morning, she notices that both eyes are red, swollen, and watering. Being concerned, she takes him to the pediatrician in the morning and is told that he has “conjunctivitis.” She is told that the infection should go away by itself. A. What part of the eye is involved? B. What type of conjunctivitis do you think this child has (bacterial, viral, or allergic)? C. Why didn’t the pediatrician order an antimicrobial drug? D. Is the condition contagious? What measures should she take to prevent its spread? 2. During a routine eye examination to get new glasses because she had been having difficulty with