Eighteen rhesus monkeys underwent lens implantation with Choyce Mark VIII, Binkhorst iridocapsular, or Shearing posterior chamber lenses. They were sacrificed 4-28 months postoperative. The eyes were compared clinically and histologically. Controls included unoperated eyes and eyes with lens extraction without implantation. Several histologic findings pertained equally to cataract extraction with or without lens implantation. Late opacification of the posterior capsule was caused by migrations and fibrous metaplasia of the lens epithelial cells. These cells appeared to undergo such metaplasia only when exposed directly to aqueous, never when they were in firm apposition to another tissue such as another layer of capsular epithelium, lens cortex, or iris. All implants were well tolerated clinically. Histologically the eyes with Binkhorst lenses showed a tendency to focal loss of iris pigment epithelium and some pigmented macrophages in the iris stroma an trabecular mesh. The Choyce lenses frequently displayed marked displacement and thinning of the iris root, and occasionally showed a few chronic inflammatory cells and thin fibrous encapsulation around the implant feet. The Shearing lenses had no effect on the adjacent ciliary body when the loops were well seated in the lens capsule, but when a loop was anterior to the capsule, it eroded into the ciliary body. The loops developed a thin fibrous capsule within the ciliary body with very little chronic inflammatory reaction. The long-term effect of such loops lying in the ciliary body is undetermined, however. At present it is recommended that, if such a lens is implanted, every effort be made to ensure both loops lie in the capsular envelope. On the basis of this study, it is also recommended that in removing such a lens, one must assume that a loop might lie embedded in the ciliary body and cut the lens free from the loops before removing it.
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A. R. Irvine (1981) studied this question.