Corrective Lens Options
What types of contacts correct for astigmatism?
- Gas Permeable (GP)
A GP lens is a semi-hard lens that is often smaller than a soft contact lens. It corrects astigmatism by acting to make the surface of the eye spherical. It does this by usually being spherical itself; one's tears fill the space between the lens and the spoon-shaped cornea. If a high amount of astigmatism is coming from the natural lens in the eye instead of the cornea, this spherical design doesn't work as well; your doctor may prescribe a more sophisticated lens such as a front-toric or bitoric design. If your eye has a lot of astigmatism, he or she may fit you with a back-toric design or other specialty lens to get a more comfortable fit.
- Soft Toric Contact Lenses
A soft toric contact lens is a hydrophilic, flexible material lens that has different powers in opposing meridians built into the lens. In order to correct for the astigmatism appropriately, the powers have to align with the right areas of the eye.
There are various designs to allow for this, but a common one is prism ballast, which has a thicker spot on the bottom of the soft lens to help hold the lens in position. Without that, or another stabilization method, the vision would be highly variable. As the patient blinks the contact lens could endlessly rotate.
- Hybrid Lenses
Beyond GP and soft toric contact lenses, there are now hybrid lenses. Hybrid lenses either have a soft lens skirt with a rigid central portion or the lens or are made of a stiffer soft lens material. The hybrid lens combines the benefits that each lens has to offer and may be best for a difficult to fit eye, like one with irregular astigmatism.
- Orthokeratology Lenses
Corneal Refractive Therapy (CRT) or Orthokeratology lenses are essentially an RGP lens worn while sleeping designed to mold the eye. The fit of the contact is such that it reshapes the cornea by pushing on the steep areas much like an oral retainer does to teeth. The flattening effect of the contact lens typically lasts all day to enable the wearer to see clearly without a lens while awake, but then the user would need to resume wear again the next night to maintain clear vision the following day. It works best for mild to moderate amounts of nearsightedness and less than one and a half diopters of astigmatism.
