Once a lens has been removed, the refractive power of the lens must be replaced so that light can focus onto the retina, the innermost layer of the eye, which consists of light-sensitive nerve tissue. The three most common replacement options are intraocular lens implants, glasses, and contact lenses.
Intraocular lens implants. By far the most frequent type of lens replacement is an intraocular lens implant, which is placed at the time of cataract surgery. More than a hundred brands of implants are available. Intraocular lens implants have been in wide use since 1977, and most ophthalmologists believe they are very safe.
The most common type of lens implant is the single-focus lens. Unlike the natural lens of the eye, a single-focus lens cannot alter its shape to bring objects at different distances into focus. As a result, the surgeon generally selects a lens that will provide good distance vision, and the person wears reading glasses for near vision. Alternately, the surgeon can correct one eye for distance and the other for near vision; this is called monovision.
In general, new eyeglasses cannot be prescribed until about three weeks after cataract surgery because the prescription changes as the eye heals. Still, if the eye is otherwise normal, people with lens implants often have functional vision as early as the first day after surgery.
The first multifocal lens implant, which provides both distance and near vision, was approved by the U.S. Food and Drug Administration several years ago. Although these lenses reduce the need for eyeglasses, many people still have to wear glasses for certain tasks. In addition, multifocal lenses can cause visual side effects such as glare and halos.
The newest type of lens implant, called an accommodating lens, contains a hinge that allows for both distance and near vision. The FDA approved the first of these devices, the CrystaLens, in 2003.
Although most people do achieve 20/40 vision or better with the implant, the range of vision varies, and improvements in near vision may decrease over time.
Once inserted, lens implants require no care of any kind. Like any device, however, complications can occur. The most common complication is glare or reduced vision when the intraocular lens is not aligned with the pupil.
Not all people who undergo cataract surgery are able to receive an intraocular lens implant, however. For example, lens implantation may not be possible in people with certain eye diseases including severe, recurrent uveitis (inflammation of the iris, ciliary body, or choroid), some cases of proliferative diabetic retinopathy (new blood vessel growth onto the back surface of the vitreous humor, the thick, gel-like substance that fills the back of the eyeball behind the lens), and rubeosis iridis (new blood vessel growth on the iris, which usually occurs in people with diabetes).
Glasses. Another option for lens replacement is cataract glasses. Although effective, these glasses are rarely used after routine cataract surgery because they are heavy and awkward. The glasses magnify objects by about 25 percent, causing them to appear closer than they actually are--a somewhat disorienting sensation. Because of the thickness and curvature of the lenses, cataract glasses magnify objects unequally and so have a distorting effect as well. In addition, they tend to limit peripheral vision.
Contact lenses. Like cataract glasses, contact lenses are not routinely used after cataract surgery. The lenses provide almost normal vision, but their major drawback is that people often have difficulty handling, removing, and cleaning them.
Both the contacts and glasses can be prescribed four to eight weeks after surgery.