Understanding Vision Problems -- the Basics
What Are Vision Problems?
Your eyes are your body's most highly developed sensory organs. In fact, a far larger part of the brain is dedicated to vision than to hearing, taste, touch, or smell combined! We tend to take eyesight for granted; yet when vision problems develop, most of us will do everything in our power to restore our eyesight to normal.
The most common forms of vision impairment are errors of refraction -- the way light rays are focused inside the eye so images can be transmitted to the brain. Nearsightedness, farsightedness, and astigmatism are examples of refractive disorders and often occur when the eyes are otherwise healthy. Refractive errors are correctable usually with glasses, contact lenses, or refractive surgery, such as LASIK.
Other vision problems may be related to eye disease. Retinal detachment, macular degeneration, cataracts, and glaucoma are disorders of the functional eye and its processing units. These problems can lead to blurry or defective vision. The goals of treatment are to halt vision loss and preserve remaining eyesight.
Here are descriptions of common vision problems.
Nearsightedness and farsightedness have to do with the way the eye brings images into focus on the back of the eyeball, where 10 layers of delicate nerve tissue make up the retina. Images that do not focus on the retina will appear blurry. The further away images focus from the retina, the blurrier they appear.
Nearsightedness, or myopia, affects about 40% of the population. It is the result of images being focused in front of the retina rather than on it, so distant objects appear blurred. A nearsighted person whose eyesight has not been corrected holds a book closer to the eyes when reading and has to sit in the front of the classroom or movie theater to see clearly. The condition runs in families and affects men and women equally, usually appearing in childhood and stabilizing in the 20s.
Farsightedness, or hyperopia, is the opposite of nearsightedness. The hyperopic eye focuses images slightly behind the retina, making nearby objects appear blurry. Children may outgrow mild farsightedness as they mature and the eyeball reaches adult size. Did you know that the eye grows during childhood? The length of the eye (from front-to-back) elongates nearly one-third between birth and age five, and the volume of the eye nearly doubles!
Light rays entering the eye first cross the clear cornea. Surprisingly, nearly two-thirds of the eye's focusing power occurs along its front surface (tear film or cornea). The normal cornea should have a semi-spherical contour similar to a soup spoon. This permits the eye to create a single focused image. If the central cornea is not symmetrical or uniform we say it is "astigmatic."
Astigmatism, often combined with nearsightedness or farsightedness, occurs when the clear cornea has a non-round curvature -- more like a teaspoon or football. Because of that, the eye lacks a single point of focus. People with astigmatism may have a random, inconsistent vision pattern, wherein some objects appear clear and others blurry. The next time you hold some shiny silverware, compare your reflection in a soup spoon to that produced by the teaspoon -- that's astigmatism! Astigmatism is usually present from birth but is sometimes not recognized until later in life. Most astigmatism is fully correctable. Also, it changes very little over time.