Comparison of shape recovery ratios of single-piece poly(methyl methacrylate) intraocular lens haptics.

We studied shape recovery ratios of several single- and three-piece intraocular lens (IOL) haptics after conducting compression tests for various lengths of time. Results of the comparison of poly(methyl methacrylate) (PMMA) IOL haptics configured of a single piece and of three pieces showed a superior shape recovery ratio for single-piece haptics. Comparisons of the shape recovery ratios among single-piece PMMA haptics and conventional three-piece haptics made of polyvinylidene fluoride (PVDF), PMMA, and polypropylene (PP) revealed that the shape recovery ratio of single-piece PMMA haptics was higher than the ratios of the conventional three-piece PMMA and PP haptics. The ratios of two of three of the single-piece PMMA haptics, however, were lower than the ratios of three-piece PVDF haptics. The form and manufacturing procedures of haptics likely have a significant impact on the shape recovery ratio of haptics, even those made of the same material. Since decentration after IOL surgery could be caused by the condition of the patient's lenticular capsule and Zinn's zonule, it is difficult to conclude that the shape recovery ratio is the only factor in IOL stability. Nevertheless, this study indicates that IOL haptics that cause less decentration and have better mechanical properties should be developed.