Aging-Related Diseases Eye - Glaucoma, Age-related Macular Degeneration, Cataracts
The sense of sight, said Aristotle is preferred "to everything else. The reason is that this, most of all the senses makes us know and brings to light many differences between things" (Metaphysics, 98A225).
If one looks an eye straight on, several important structures are recognizable, including the pupil, which is the black circle in the center of the eye that dilates and constricts in response to light; the iris, which is the colored muscular structure that allows the pupil to change its size; the transparent cornea, which is really the window of the eye; and the lens. The latter focuses light through the pupil onto the retina at the back of the eye, much as a lens in a camera focuses images onto film. Images are then transformed into electrical signals that are transmitted to the visual cortex at the back of the brain. The space in the eyeball between the lens and the retina is filled with a viscous clear liquid known as vitreous humor (see Figure 1).
With age, many changes (some virtually universal, and others arising from age-related disease) threaten the quality of vision. For instance, tear glands often work less well, leading many older adults to suffer from dry eyes (easily treated with artificial tears). Lax muscles around the eye can result in the lower lid margin rotating away from the eyeball (ectropion) or an inward migration of the eyelashes and eyelid toward the globe (entropion). In the conjunctiva (the skin on the inside of the lid and covering the white part of the eye), tiny blood vessels can rupture, giving rise to localized accumulation of blood akin to a bruise (subconjunctival hemorrhage). Though unsightly, it is not serious and usually does not signify any underlying disorder. It can clear up spontaneously in six to eight days.
Particularly in people who are near-sighted, "floaters" (tiny, condensed debris floating in the vitreous humor) are common and of little consequence. However, any sudden increase in the number of floaters, particularly if accompanied by flashing lights, can herald the onset of serious retinal problems, and requires a thorough eye examination as soon as possible.
Other age-related eye problems can also threaten vision and require evaluation by an ophthalmologist. Corneal ulcers, tumors on or near the eye, inflammation of the structures of the eyeball, occlusion of retinal vessels, and any sudden loss of vision are among them.
Three common sight-threatening disorders are described here in more detail. Each can result in problems sufficient to meet the World Health Organization's definition of visual impairment (i.e., visual acuity less than 20/60 in the better eye). Overall, about 2–4 percent of the population age seventy and over suffers from such impairment.
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