Toric lens implants are used to correct astigmatism at the time of cataract or other intraocular lens surgeries. Astigmatism is a name given to describe the shape of the cornea. The cornea is the clear front layer of the eye responsible for two thirds of the eye's focusing power. When the cornea has a spherical shape, astigmatism is absent. When the cornea is not spherical it is said to have astigmatism. A cornea with astigmatism will create two zones of focus which is generally perceived as blurring of vision.
Astigmatism is measured during preoperative assessments by instruments that evaluate the shape of your cornea, known as keratometers and topographers. Most individuals have some astigmatism and its significance is determined by the amount measured in diopters. Low but significant to very high degrees of astigmatism now can be lessened with toric lens implants.
Toric lenses are designed to be positioned on the axis of astigmatism to neutralize its effect. If the target reduction of astigmatism is not achieved it will usually be due to a slight misalignment of the lens. Despite meticulous alignment at the time of surgery a slight rotation of the lens implant may occur within the first day of the procedure in about 5% of procedures. Because the effect of the toric lens in astigmatism correction depends on a precise match of both lens implant and corneal astigmatism meridians this rotation may lessen achieved astigmatism correction. If this were to be significant, a short "touch-up" procedure in the operating room would be required to restore the best orientation of the lens implant and correction of astigmatism.