Then, when the toric IOL is implanted during the cataract procedure, the surgeon rotates the IOL so the markings on the IOL are aligned with the markings on the cornea to insure proper astigmatism correction.Prior to the development of toric IOLs, cataract surgeons had to perform a procedure call limbal relaxing incisions (LRI) to correct astigmatism during or after cataract surgery.In LRI, small incisions are made at opposite ends of the cornea, very near the junction between the cornea and the surrounding white sclera.(This junction is called the limbus.) When these incisions heal, the cornea becomes more spherical in shape, reducing or eliminating astigmatism.
Traditional intraocular lenses have a spherical optical design, meaning the front surface is uniformly curved from the center of the lens to its periphery.Conventional spherical IOLs are monofocal lenses, meaning they are designed to provide clear vision at a single focal point (usually far away for good driving vision, for example).With conventional IOLs, typically you must wear eyeglasses or contact lenses in order to use a computer, read or perform other close-up tasks within arm's length.Though a spherical IOL is relatively easy to manufacture, this design does not mimic the shape of the natural lens inside the eye, which varies in curvature from center to periphery.In other words, the eye's natural lens is aspheric ("not spherical"). A spherical intraocular lens can induce minor optical imperfections called higher-order aberrations (HOAs), which can affect quality of vision, particularly in low-light conditions such as driving at night.In some cases even when a toric IOL is used limbal relaxing incisions may be needed after cataract surgery to fully correct astigmatism.