Contact lenses are not all made the same. Standard contact lenses correct for either nearsightedness (myopia) or farsightedness (hyperopia). These lenses are "spherical", containing one uniform power across the lens. But for those persons who have corneas with astigmatism, a condition causing light to focus on more than one point behind the cornea, specialized contact lenses are needed.
Toric contact lenses are lenses that contain both a curvature to correct for myopia or hyperopia as well as the additional curvature that corresponds to the where the cornea is more curved, the most common cause of astigmatism. These lenses are often weighted to maintain proper alignment on the cornea. Toric lenses are available in soft and firm gas permeable contact lens designs. For patients with high amounts of astigmatism, firm gas permeable lenses usually give crisper vision since they are specifically made for an individual, taking into account very high amounts of corneal curvature.
Many patients do not need to wear toric contact lenses just because they have astigmatism. With small amounts of astigmatism, a slightly higher-powered spherical soft contact lens can be used to compensate for the additional corneal curve. Due to their design, spherical gas permeable lenses can sometimes correct for smaller amounts of astigmatism because they "float" on a bed of tears, forming a "lens" between the contact lens and cornea, thus providing the additional power required to see well.
Both soft and firm gas permeable toric lenses are available in bifocal or multifocal designs for patients over 40 who need help seeing up close as well. Most of the soft toric contact lenses are disposable or frequent replacement lenses and changed on a two week, monthly or quarterly schedule.