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Physiological Changes in Major Organ Systems

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Older adults develop significant age-related changes in the eye, which have important effects on vision. The weakening of the ciliary muscle, combined with decreased curvature of the lens, results in a loss of accommodation; therefore, it becomes difficult for an individual to focus on near objects, and bifocals may be needed. It is also difficult for elderly people to adapt to light because of rigidity of the pupil and increasing size and opacity of the lens. As the lens changes with age, the increased scattering of light produces glare, which may be bothersome to elderly people. The pupil becomes smaller in diameter (more miotic) with age, due to atrophy of the dilator muscle fibers and increased rigidity of the blood vessels of the iris. This anatomical alteration in the pupil, combined with the increased thickness of the lens, contributes to the impairment of the visual performance of older persons at twilight. The growth in lens thickness causes a change in the absorption of light, with a decreased sensitivity at the violet end of the spectrum and a decreased ability to distinguish between blues and greens. Elderly people also show a decline in their ability to view objects at rest (static acuity) and in motion (dynamic acuity). Reportedly, 93.5% of individuals ages 40–44 years have a corrected visual acuity of 20/20 or better compared with 41.9% of those ages 70–74 years (Weymouth 1960). With age, the lens opacifies (i.e., becomes less transparent as a result of protein aggregations), and a cataract can form. Elderly patients are also at risk for age-related macular degeneration, which causes loss of central vision when drusen (yellowish-white deposits) accumulate in the retina. Age-related macular degeneration is the most common cause of blindness in elderly people (Haegerstrom-Portnoy and Morgan 2007; Harvey 2003).

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