Toric contact lenses may be needed to treat astigmatism.
Astigmatism is very common, but why the cornea or lens differs in shape from person to person is unknown. The likelihood of developing astigmatism seems to be inherited. Astigmatism can also develop after an eye disease, eye injury or eye surgery.
Many cases of astigmatism can be corrected with soft toric contact lenses, rigid gas permeable contact lenses, or hybrid contact lenses.
Soft Toric Contact Lenses
The term toric means the contact lens has different corrective curves, optical powers, and focal lengths in two orientations perpendicular to each other. To correct the imperfect curvature that is an astigmatism, the toric lenses must stay oriented in the right position.
To keep toric contact lenses in the correct position on the eyes they are designed with special features:
- Thin-thick zones
- Lens truncation in which a portion of the bottom of the lenses are cut off
- Ballasting, in which the lenses are heavier in places
Soft toric contact lenses for astigmatism are made of either hydrogel material or highly breathable silicone hydrogel material. Both types are made of plastics that are hard when dry but readily absorb water and become soft and gel-like when hydrated. Silicone hydrogel increases the oxygen permeability of the contact lens.
Silicone hydrogel with its enhanced oxygen permeability make them a good choice when the lens design requires greater mass, such as toric contacts, bifocal contacts, and other hard-to-fit, or custom contact lens designs.
Gas Permeable Contact Lenses
Rigid gas permeable contacts lenses are another popular option for correcting astigmatisms. In most cases rigid gas permeable contact lenses can correct astigmatism without a toric design. This is because the lenses are rigid and retain their spherical shape instead of conforming to the eye’s irregular shape.
The rigid and uniform shape of the lenses becomes the primary refracting surface and thereby corrects the astigmatism. For higher degrees of astigmatism, a special large-diameter gas permeable contact called scleral lenses can be used to correct very irregular corneal surfaces.
Fitting gas permeable contact lenses takes more time and expertise than fitting soft contact lenses.
Hybrid Contact Lenses
The center portion of hybrid contact lenses are made of rigid gas permeable lens material and the outer portion of the lens is made of a soft hydrogel or silicone hydrogel material. These lenses can provide the best of both types—the sharp vision of a gas permeable lens with the comfort of a soft lens.
Fitting hybrid contact lenses takes more time and expertise than fitting soft contact lenses and hybrid lenses are custom-made for each wearer’s eyes. This makes them more expensive, but they don’t need to be replaced as frequently as soft lenses.
Schedule an Exam
If you have astigmatism and want to wear contact lenses, have a comprehensive eye exam and a contact lens consultation to find out if you are a good candidate for contact lenses and which type of astigmatism-correcting lenses will work best for you.