Myopia

Myopia is the refractive condition where the farthest point of focus is located at a point near to the observer, and not at infinity. When one is nearsighted, distance vision is blurred at all times while near vision is often excellent within a certain range. There are a number of explanations for this optical condition. The eyeball may be too long, causing the image to be focused short of the retina at the back of the eye. Or, the focusing lenses of the eye are too strong.

The primary focusing lens is the cornea, the clear window at the very front of your eye. The internal lens, called the crystalline lens, is adjustable and alters your focus from distance to near. Sometimes, one of these two lenses may have a radius of curvature that is too steep. In myopia, it is often the cornea that is too highly curved. It is this curvature which is altered in the refractive surgery techniques now becoming available. See Abstracts: Refractive surgery.

Shortening the eyeball has been tried, but it has not been without the potential of serious and permanent damage. Of course eyeglasses and contact lenses are still the safest and most practical optical remedies. The lens power, whether it be in spectacles or contact lenses, is a minus power, which cancels the excessive plus power of near-sightedness. The image now comes to a clear focus at the back of the eye.

Exercises and manipulating lens corrections are sometimes effective in reducing the degree of myopia. They are more effective for children or for adult onset, stress related near-sightedness. For example, an adult who had perfect vision and starts an activity requiring intensive near vision tasks may complain of blurred distance later in the day. The assumption here is that there are situations where the crystalline lens is forced into an excessive plus power curvature. This may occur from near vision stress, a spasm of the ciliary muscle, diet, medications, even emotional fatigue. Exercises which help to relax the muscle and training the focusing system may indeed resolve the problem. On the other hand, remedies for long-standing, childhood onset, high levels of myopia are very rarely effective. Believers of certain controversial exercise programs will take objection to this statement and there are often lively discussions of this issue in the Usenet news groups sci.med.vision and misc.health.alternative.

Finally, myopia may be combined with other optical corrections, including astigmatism and presbyopia.