Contact Lenses Care

The lens in your eye can only adjust so much in an effort to bring objects into focus. When the eye can’t focus properly, there are four basic conditions that may be the cause. These are called refractive errors (myopia, hyperopia, astigmatism, and presbyopia). Luckily, all are correctible with contact lenses or spectacles. Most of these refractive errors are a result of heredity.

Nearsightedness (Myopia). This occurs when the eyeball is too long for the lens’s focal capacity. The patient’s cornea and lens focus the image of a distant object in front of the retina, so vision is blurry except when looking at nearby objects. Myopia affects one quarter of the world and seems to be on the rise, though it’s a mystery why. Most contact lens wearers are myopes.

Farsightedness (Hyperopia). This occurs when the eyeball is too short. As a result the lens of the eye can’t bring near objects into focus by the time the image reaches the retina. (Theoretically the focal point is behind the retina.) Therefore close objects are blurry, and distant objects are clear. In mild cases distant objects are seen clearly enough so constant visual correction is not required. In severe cases distance vision may also be affected, so the hyperope needs to wear some form of vision correction constantly; these are more likely candidates for contact lenses, though the percentage is far lower than for myopia.

Astigmatism. This is a bit harder to understand. Astigmatism is a refractive error that usually results from a cornea that isn’t perfectly round, but shaped more like a football than the usual basketball shape. Imagine the cornea as a dome divided into segments by lines drawn across its surface that intersect at its center, like the segments of an orange. The normal eye, with a spherical cornea, has the same curved lines all around. The astigmatic’s  aspherical cornea has differently curved lines like one half of a lemon, with any given line either flatter or steeper than the one perpendicular to it. Therefore the vertical and horizontal components of both near and far images can’t focus together. As a result the image appears blurry. Occasionally the crystalline lens—not the cornea—is at fault in astigmatism. Astigmatism is very common and often occurs in addition to myopia or hyperopia.

Presbyopia. This is part of the aging process (usually after the age of forty) and is due to the gradual loss of elasticity of the crystalline lens of the eye. As the lens loses its flexibility, one has more and more difficulty focusing on nearby objects. You’ll know your eyes are “getting old” if your arms seem too short when you read, or if you have trouble performing close-up tasks like threading a needle. Presbyopia will occur in addition to the “Big Three”—myopia, hyperopia, and astigmatism—but pure presbyopes only require a correction during close-up tasks.

Nearly half our population has one or more of these refractive errors. Fortunately all of them can be corrected witheyeglasses or contact lenses. In nearly all cases the contact lens does it better.

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