GP Contacts Easily Correct Astigmatism
Astigmatism creates multiple points of focus from light entering the eye. This results in blurred vision, which is correctable with contacts or glasses.
Astigmatism simply means that the eye is not perfectly round or spherical. The vast majority of people have some degree of astigmatism, but in most cases, the astigmatism is so minor there's no need to compensate for it with special eyeglasses or contact lenses.
More significant amounts of astigmatism require correction for good vision. To accomplish this, your glasses or contacts will have a certain refractive correction in one meridian of the lens and a different correction in the meridian that's 90 degrees away.
For example, if the thickness of your glasses is greater at the edge of the vertical meridian than the edge of the horizontal meridian, it means that the vertical meridian has a higher nearsighted correction than the horizontal one. If your glasses prescription is -6.00 - 1.50 x 180, it means that you need -6.00 diopters of correction in one meridian and -7.50 diopters in the other meridian. The difference (-1.50 diopters) is the amount of astigmatism.
GPs and Astigmatism
Because almost all (if not all) astigmatism results from the front surface of the cornea, GP lenses are an ideal solution. Because it is rigid, a GP can mold the tear film on the front of the eye into a spherical shape. This will correct the astigmatism, resulting in very good vision.
In very high astigmatism, a so-called "bitoric" lens design can be used that has a different back surface curve in each meridian to provide a better fit, as well as good vision.
Soft Lenses and Astigmatism
A conventional soft lens, because it simply drapes over the cornea, does not correct astigmatism.
A special-design soft "toric" lens does correct for astigmatism with a curvature that's often manufactured onto the front surface of the lens. However, if this lens rotates while blinking, vision will be temporarily blurred. This problem worsens as the astigmatism correction increases.
Study Says Lens Wearers Prefer GPs for Astigmatism
A recent study published in Optometry (the Journal of the American Optometric Association) found that when soft toric lenses and bitoric GP lenses were both worn for one month each by highly astigmatic participants, almost 75% said the vision was better with GP lenses.
In addition, although only about 10% of the subjects wore GP lenses prior to the study, almost 60% ended up wearing GP lenses once the study had concluded.
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[Page updated February 2013]