Toric lenses correct both refractive errors due to near- or farsightedness and visual dysfunction due to astigmatism. These lenses exist in rigid, gas-permeable (RGP) form and as soft lenses. According to the American Association of Optometrists, 20.1% of contact lens wearers in the US were prescribed with toric lenses in 2007.
The first toric Lenses which came on the market were not as reliable or comfortable as ordinary lenses. Now there are lenses available in both a comfortable and easy to use format. In fact, extended wear toric lenses that can be worn up to 30 days at a time are now prescribed relatively commonly to new and experienced CL customers. Even tinted lenses, daily disposable and progressive lenses are now available in toric form.
How do toric lenses work? This type of lens contains two powers, one that corrects for a spherical refractive error and another that re-configures light rays that are unevenly refracted due to astigmatism. Because the astigmatic correcting element is closely linked to a particular axis of orientation or "angular direction", it is extremely important that toric lenses stay centered correctly on the cornea. An extra weight or ballast in the lower section of each lens combined with the eye’s normal propensity to blink often help to ensure correct centration.
A person’s degree of astigmatism often increases with age. A customer with a very high degree of astigmatism will often be recommended for wavefront laser surgery since this method is significantly more precise in mapping out and correcting the uneven sections of the cornea.
2 Fitting and Vision Characteristics of Two Silicon Hydrogel Torics Reineld, Bill O.D.
www.clspectrum.com/article.aspx?article=101851 (July 2008)