ASTIGMATISM MADE EASY
Most of my patients think that astigmatism is a disease; it is not and it’s time to clear the air. Astigmatism is a normal condition effecting 80 percent of the population. Astigmatism is caused by an irregular shape of the cornea; the clear window on the front of the eye is the cornea. In a non-astigmatic eye it has a round curve in all directions, like a basketball. In the case of astigmatism, it is shaped like a spoon. In one direction there is a steep curve and in the other there is a gentle curve. This is called “regular astigmatism.” When light passes into the eye it must pass through the cornea. When there is no astigmatism the light comes to a perfect focus on the retina and the vision is excellent. When light passes through an astigmatic cornea light from different directions is focused differently and there is a blurry image projected onto the retina.
Regular astigmatism is easily corrected with eyeglasses or contact lenses. If you hold your glasses out in front of you and look at a picture on the wall while rotating the glasses you might see some changing distortion; this is the lens correcting your astigmatism. Rigid gas permeable (hard) contacts are excellent at correcting astigmatism while soft lenses are less effective.
There are excellent surgical techniques for the correction of astigmatism. The oldest method that I began using in 1982 is astigmatic keratotomy. Here small straight incisions are made on the cornea across the steeper curve (meridian). This tends to flatten that meridian and steepen the flatter meridian, ultimately making the cornea more spherical. Along came LASIK where after several years there emerged an algorithm for the correction of astigmatism along with nearsightedness and eventually along with farsightedness. Very substantial amounts of astigmatism can be corrected with LASIK. More recently, we have added a variation of astigmatic keratotomy (AK), known as limbal relaxing incision (LRI). Here the corneal incision is moved to the outer edge of the cornea and is curved rather than straight. It is more predictable than AK.
When patients come for cataract surgery we always evaluate their astigmatism. This is done so that we can calculate the power of the lens to be implanted at surgery and also to be in the position to offer them an opportunity to have the astigmatism corrected with LRI at the same time. The purpose is to enable patients to achieve excellent vision without glasses when the cataract surgery is done. We usually reserve the LRI for small amounts of astigmatism because there now is available the toric lens. This is an intraocular lens with optics designed to neutralize the astigmatism along with the correction of myopia or hyperopia. This lens is implanted just as any lens might be then it is rotated into a position to match the steep meridian on the cornea, thus neutralizing the astigmatism.
So don’t be concerned when you learn that you have astigmatism; it could be a lot worse.
Tags: astigmatic keratotomy, astigmatism, cataract surgery, contact lens, cornea, eyeglasses, hyperopia, LASIK, limbal relaxing incisions, LRI, myopia, retina, toric lens
