The process described above works best if the eye is a perfect sphere and the cornea is smooth and rounded. Often this isn't the case. The eye might be shorter or longer from front to back than it is from top to bottom, or the cornea's curvature might be slightly flattened.
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| How To Get Better Eyesight Without Glasses |
Farsightedness and Nearsightedness
If your own eyes are shorter than normal from front to back, then you have hyperopia, or farsightedness, and you see distant objects more clearly than near ones. If the opposite is true - your eyes are too long from front to back - you have myopia, or nearsightedness, and you have trouble seeing distant objects.
Astigmatism
The cornea's curvature should be rounded, like the side of a basketball. If, instead, it's shaped more like the side of a football, it will produce two focal points instead of just one. This condition is called astigmatism and it causes blur and distortion, especially up close.
Cataracts and Lens Function
You can see how many structures and processes are important to the act of seeing. If just one structure is defective or one process doesn't work properly, the eyesight - so important to most of us in almost everything we do - can be damaged. Like other parts of our bodies, our eyes don't function as well when we age as they did when we were young.
Cataracts are the most common age-related eye defect.
What Is a Cataract?
If you're in your mid-fifties or older, there's a good chance that your eyes have started to develop cataracts. You can't see them, you can't feel them, and until they begin to seriously affect your vision you don't really need to do anything about them except continue to take good care of your eyes. That means having regular eye exams and protecting your eyes - from injury, from the sun's ultraviolet (UV) rays, and from irritants such as dust and wind.
A cataract is a clouding of the natural lens inside the eye. The clouded areas are often called opacities because they are opaque, meaning they are not clear, and light cannot pass through. The lens must be crystal clear to do its focusing job, so the areas of opacity interfere with good vision.
What Causes Cataracts?
Protein fibers in the lens, called crystallines, are precisely arranged in thousands of layers. Usually because of aging, the proteins deteriorate or become "disarranged." Some scientists believe that these fragmented proteins cause the densities, or "clumps," that cloud areas of the lens. These dense areas are cataracts, and as they become larger they cause noticeable vision loss.
People sometimes confuse cataracts with an unrelated lens condition, presbyopia - a stiffening of the lens also caused by aging. Throughout life, the lens continues to manufacture new layers of cells, and the accumulation of layers makes the lens less pliable. As the lens loses its flexibility, it also loses the ability to accommodate as well as it once could.
At about age forty-five, most people - even those who have had excellent vision - find that "their arms are too short." They have to hold books and magazines farther from their eyes in order to focus on the print. If presbyopia is your only vision problem, you can probably solve it with inexpensive reading glasses.
Types of Cataracts
You will usually see cataracts classified according to their location on the lens: nuclear, cortical, or subcapsular. A nuclear cataract is the most common and is the type most associated with aging, although older patients often have more than one type.
Nuclear Cataracts
A nuclear cataract, as the name suggests, is a clouding of the center of the lens, almost always due to aging. One of the early symptoms, oddly enough, is that your near vision will improve for a while. This improvement, referred to as second sight, is short-lived, however. As the cataract advances, the lens becomes yellow or even brown. Vision becomes dimmer and blurrier, and you're likely to have trouble distinguishing colors. Glare might bother you, making it hard to drive at night. You may need stronger light for pursuits such as reading and needlework. To find out more, you can check out How To Get Better Eyesight Without Glasses.