Extracapsular cataract extraction retains an intact posterior capsule, a portion of the anterior capsule, and the lens equator. As previously described, there is a region of epithelial cells that proliferate and migrate along the posterior capsule. When this occurs to a significant extent, the visual axis is obscured and results in reduced visual acuity (Obstbaum, 1988). Since some degree of capsular opacity frequently develops, this event is considered to be a consequence rather than a complication of extracapsular surgery.
Several ways to reduce the incidence of capsular opacification have achieved moderate success, but at best, they only retard the progression of opacification. Complete inhibition of cellular metaplasia and migration, however, has not yet been accomplished, although promising work using monoclonal antibodies directed against lens epithelial cells is being investigated. At present, it appears that placing PMMA firmly against the posterior capsule slows the rate of posterior capsule opacification related to epithelial proliferation but not that caused by fibrosis (Lindstrom and Harris, 1980; Downing, 1986; Sterling and Wood, 1986; Sellman and Lindstrom, 1988; Hansen et al., 1988). IOL designs that accomplish this type of apposition are those with biconvex and reverse optics. There is further evidence that angulated haptics that push the posterior surface of the optic more tightly against the posterior capsule enhance this effect (Downing, 1986). It has also been suggested that capsular bag implantation of the IOL retards capsular opacification, perhaps by contributing to the barrier effect.
A benefit of fibrosis in the peripheral region of the capsular bag is that if keeps the IOL in position. Although fibrosis is associated with capsular opacification, an undesirable effect, it also helps retain the stability of the IOL. If a method evolves that completely removes the epithelial cells, the incidence of capsular opacification will decrease, but so will the desired stabilizing effect. We will then require lens designs that maintain the IOL in its proper position independent of capsular fibrosis.
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