Chapter 6 Special Sensory Organs: Eye and Ear 259 Diseases and Disorders Diseases and disorders of the special sensory organs range from the mild to the severe, and they have a wide variety of causes. We will briefly examine some problems that commonly affect the eye and the ear. The Eye The eyes are among the most delicate organs of the body. Some eye condi- tions, such as minor infections, are short lived. Others require corrective treat- ment such as eyeglasses, contact lenses, or surgery. Left untreated, serious eye conditions—especially those linked with systemic pathology (for example, diabetic retinopathy)—can result in permanent loss of vision. Astigmatism Astigmatism (ă-STĬG-mă-tĭzm) is a common condition that causes blurred vision due either to an irregularly shaped cornea or curvature of the lens (Figure 6.3). An irregular-shaped cornea or lens prevents light from properly focusing on the retina. As a result, vision becomes distorted or blurred at any distance, causing eye discomfort and headaches. Astigmatism is often present at birth and may occur in conjunction with myopia or hyperopia (Figure 6.4, on the next page). Myopia (mī-ŌP-ē-ă), more commonly known as nearsightedness, is a condition in which close objects are seen clearly, but objects farther away appear blurred. Hyperopia (HĪ-pĕr-ŌP-ē-ă), or farsightedness, is a condition in which distant objects are usually seen clearly, but close ones do not come into proper focus. Together, myopia and hyperopia are referred to as refractive errors because they affect how the eyes refract, or bend, light. The specific cause of astigmatism is unknown. Iris Pupil Cornea Astigmatic cornea A. Normal Vision B. Astigmatic Vision Figure 6.3 Astigmatism, the result of an irregularly shaped cornea or curvature of the lens, prevents light rays from properly focusing on the retina, causing blurred or distorted vision.
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