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If you have astigmatism you may have heard that contact lenses cannot solve your problem. While it used to be true that some contacts could not correct astigmatism, there are now several options in contact lenses that can help you see clearly.
Anatomy of astigmatism
The cornea is the clear front part of the eye covering the pupil. When light enters the eye, it first passes through the cornea, then through the pupil and lens and lands on the retina which is the lining on the inside back of the eye.
Astigmatism is caused by an irregularly shaped cornea or lens in the eye. When light passes through a cornea that is not uniformly round, the light does not all focus at the same point inside the eye and vision is blurry. The amount of astigmatism can vary from barely noticeable to very severe. You can find out if you have astigmatism by asking your eye care professional or by looking at your glasses prescription. If your prescription has three numbers instead of just one, you have astigmatism.
How do contact lenses correct astigmatism?
Contact lenses are small disks of plastic that are carefully shaped to help correct the errors in where the light focuses on the retina. For patients without astigmatism, contact lenses are uniformly round with a smooth curve like a ping pong ball. But for patients with astigmatism, the contact lens must compensate for the irregularities in the cornea.
For many years, the only contact lenses available to correct astigmatism were hard lenses, which are now known as rigid gas permeable or RGP lenses. Because the plastic in these lenses doesn’t change shape, the cornea of the eye is encouraged to adjust to match the shape of the lens, resulting in clearer vision and astigmatism correction.
Special soft contact lenses called toric lenses are also available to correct astigmatism. Toric lenses are made from the same material as regular soft contacts. They are specially designed to have two different curves at different angles which enables them to correct both astigmatism and either farsightedness or nearsightedness. In order for these lenses to work, they cannot rotate in the eye. So they are “weighted” on one side to keep them from rotating.
RGP or Soft – which lens is right for me?
Some patients prefer RGP lenses because they can provide sharper vision than soft lenses. Rigid gas permeable lenses can also provide a better flow of oxygen through the lens to the eye, which can help protect the health of the cornea. The downside is a loss of comfort with rigid lenses, and the inability to wear them overnight.
Soft toric lenses are believed by many patients to be more comfortable than RGP lenses. They are available from many manufacturers and depending on your prescription, may be available as frequent replacement, disposable, and daily disposable lenses. The downside of toric lenses is a possible loss of clarity compared with RGP lenses, and a higher price tag. Fitting toric lenses is more complicated than fitting either regular soft lenses or RGP lenses, so you can expect a longer visit at the eye doctor and a higher cost.
A third option in lenses combines the best of both RGP and soft lenses. Hybrid lenses consist of a RGP lens in the center to provide clear vision correction and maximum oxygen transfer to the eye. A soft “skirt” around the edges of the RGP lens adds the comfort that soft lenses provide.
If you are considering contact lenses to correct astigmatism, talk to your eye doctor to find out which lenses will work best for your prescription.
Sources:
All About Vision: Astigmatism
University of Michigan Kellogg Eye Center
All About Vision: Toric Contact Lenses
Eye Care America
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nice definition...
May 19, 2012 - 5:29amThis Comment