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Last Updated: Sunday, 23 August 2015 10:48

Written by Dr. Donald H. Mershon

BASIC  PDF in progress

Summary: As we age, most of us notice that our seeing isn't what it used to be. There are many reasons for why it can sometimes be more difficult to see what we wish. Let's consider some of the changes that can occur as we get older. Among the concerns that develop are the need for more light and the difficulty with seeing clearly, no matter where we may hold a book or other object at which we want to look. Some problems are widely discussed; others are usually not.

Perhaps most familiar are the conditions that are labeled "macular degeneration." In essence, the critical, light-sensitive tissues at the rear of the eyeball can deteriorate. If they do so, then vision will be affected and we may eventually lose sight in a central area that is normally available for tasks that require our sharpest vision. Although the retina can deteriorate or be damaged beyond the region known as the macula, degeneration of the macula itself mostly interferes with seeing in a roughly-circular central region with a diameter approximately the same as two widths of one's palm, held at arm's reach.

Macular degeneration occurs in two main forms – the "dry" form that is more common (and for which there is currently little to be done) and the "wet" form (for which vision loss can often be stopped or even reversed). In the wet form of MD, fluid gathers beneath the retina and can lift sensitive cells ("cones" and "rods") away from their normal position. Such fluids can ultimately cause the cones and rods to die. If diagnosed early enough, however, injections into the affected eye can change the situation, prevent further loss, and even restore some of the person's vision. Repeat injections may be necessary, but improvements may involve multiple lines on the standard eye chart. (My father-in-law, who was nearly 90 years-old at the time, went from no longer being able to read, to being able to read any book with moderately large type. Results, of course, do vary.)

Perhaps the second-most familiar problem is cataracts. Put briefly, each eye contains a crystaline lens which, along with the cornea of the eye, focuses light from the world onto your retina. If the retina is intact, then the better the focusing, the greater the clarity of the image and the quality of your seeing. When a cataract develops, portions of the internal proteins that form the lens alter their chemical structure. Instead of being transparent to incoming light, some of the lens degrades to being merely translucent. That is, although the light may still be allowed to pass, rays may suffer from scattering. Such scattering will decrease clarity and often results in annoying glare effects when looking at bright objects, especially when the object is seen in a setting where it contrasts with its surround (e.g., car headlights at night). As cataracts advance, they may worsen and become dense enough to reduce vision to only the discrimination of dark vs light

Cataracts by themselves, however, need no longer be a major source of vision loss. There have been years of surgical developments that can solve the problem and restore vision. Many individuals even declare that removing their cataracts is the "best thing since sliced bread!"(The article on solutions for cataracts goes into more details.)

Although less well known by the general population, the following situation will almost certainly bring back memories which demonstrate other changes. Specifically, many of us may recall from when we were youngsters that older adults would tell us to turn on (or turn up) our reading light to avoid damaging our eyes; we also recall that the amount of light seemed fine to us.

Changes that cause such intergenerational disagreement may be rooted in the fact that less and less light gets to the retina as the eye ages. Over time, the vitreous fluid (vitreous "humor") that fills the rear-most chamber of the eye accumulates left-over cellular debris. This material increasingly blocks light from reaching the retina.

At the same time, particles of the pigments that ordinarily populate the eye's, giving it its color, migrate to the cornea. As these particles gradually deposit on the inside surface of the cornea, they will result in a general graying in the eyes' outward appearance to others, as well as producing a further decrease in the amount of light that reaches the retina.

One estimate is that a 60-year-old eye requires approximately 5 times the amount of environmental light to ensure that a given amount arrives at the cones and rods. It's no wonder then that children (and teenagers) may disagree quite vehemently about the proper illumination.