Silicone IOL biocompatibility--not all silicone is the same.

In their recent paper, Chang and coauthors 1 suggest that silicone lenses should be avoided in phacotrabeculectomy on the basis of their retrospective study of cellular precipitates on intraocular lens (IOL) surfaces. Their finding of statistically increased giant cell precipitates on plate-haptic silicone IOLs (Chiron C10UB) compared with poly(methyl methacrylate) (PMMA) is consistent with the findings of a 1998 randomized study by Hollick and coauthors comparing a 3-piece silicone IOL (Iolab L141U) with a PMMA lens. At first glance, these findings seem to be contradicted by 2 prospective randomized specular microscopy studies that show epithelioid cell deposits on silicone IOLs to be almost zero and far lower than on PMMA IOLs. These latter studies examine the Allergan SI-30 3-piece silicone IOL. The Samuelson and coauthors phacotrabeculectomy study, which the authors cite in their article, offers an explanation of this discrepancy. This single-surgeon randomized study of 3 IOL types showed that first-generation silicone plate-haptic IOLs (Chiron C10/C11) had the greatest number of giant cell deposits, while the second-generation silicone IOLs (Allergan SI-30/SI-40) had the fewest. The Alcon AcrySoft was in between. Collectively, all 5 studies suggest that second-generation silicone material (e.g., SI-30), with its higher refractive index and thinner optic, is more biocompatible than first-generation silicon material (e.g., C10UB, L141U). The same dichotomy has been shown in the posterior capsule opacification (PCO) rate of different silicone IOLs. In randomized studies using photographic comparisons, first-generation silicone (Iolab L141U) was statistically inferior to the AcrySof IOL, while second-generation silicone (SI-30 IOL) was statistically superior to PMMA and equal to the AcrySof in terms of PCO reduction. Clearly, it is inaccurate and confusing to categorize all silicone materials and designs together. The conclusions of this most recent study should be limited to first-generation plate-haptic silicone rather than to all silicone IOLs.