Porth's Essentials of Pathophysiology, 4e

he special senses allow us to view and hear what is going on around us, to maintain our balance, and to communicate effectively with others. This chapter focuses on the eye and disorders of vision; the ear and disorders of hearing; and the vestibular system and dis- orders of equilibrium and balance. The Eye and Disorders of Vision There are 286 million people worldwide who are visu- ally impaired—38 million are blind and 248 million have partial vision loss that cannot be corrected. 1 Disorders of vision can result from a number of conditions includ- ing those that affect the lens (cataract), retina (retinopa- thy and macular degeneration), and intraocular pressure (glaucoma) (Fig. 38-1). General Structure of the Eye The optic globe, commonly called the eyeball, is a remarkably mobile, nearly spherical structure contained in a pyramid-shaped cavity of the skull called the orbit. The eyeball is composed of three layers: an outer layer, which includes the white, opaque sclera and the transpar- ent cornea; a middle vascular layer called the uvea , which includes the choroid, ciliary body, and iris; and an inner neural layer, which includes an outer pigment epithelium and an inner neural retina (Fig. 38-2). 2 Exposed sur- faces of the eyes are protected by the eyelids, which are mucous membrane–lined skin flaps that provide a means for shutting out most light. Tears bathe the anterior sur- face of the eye, keeping the conjunctiva and corneal epi- thelium moist and washing away foreign material. Disorders of Special Sensory Function: Vision, Hearing, and Vestibular Function 38 C h a p t e r T

The Eye and Disorders of Vision General Structure of the Eye Disorders of the Conjunctiva and Cornea Conjunctivitis Corneal Trauma Keratitis Disorders of the Lens Disorders of Refraction Disorders of Accommodation Cataracts Disorders of the Retina Retinal Blood Supply Retinopathies Retinal Detachment Macular Degeneration Disorders of Intraocular Pressure

Open-Angle Glaucoma Angle-Closure Glaucoma Congenital and Infantile Glaucoma Disorders of Neural Pathways and Cortical Centers Disorders of the Optic Pathways Visual Field Defects The Extraocular Eye Muscles and Disorders of Eye Movement Strabismus Amblyopia The Ear and Disorders of Auditory Function Disorders of the External Ear Impacted Cerumen Otitis Externa Disorders of the Middle Ear and Eustachian Tube Eustachian Tube Disorders Otitis Media Otosclerosis Disorders of Inner Ear and Central Auditory Pathways Tinnitus Central Auditory Pathway Disorders Hearing Loss Conductive Hearing Loss Sensorineural Hearing Loss Diagnosis and Treatment of Hearing Loss Hearing Loss in Infants and Children Hearing Loss in the Elderly The Vestibular System and Disorders of Equilibrium The Vestibular System Nystagmus Vertigo Disorders of Peripheral Vestibular Function Benign Paroxysmal Positional Vertigo Acute Vestibular Neuronitis Ménière Disease Disorders of Central Vestibular Function Tests of Vestibular Function Treatment of Vestibular Disorders

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