Evaluating and defining the sharpness of intraocular lenses: Microedge structure of commercially available square-edged hydrophilic intraocular lenses

PURPOSE: To evaluate the microstructure of the edges of currently available hydrophilic acrylic intraocular lenses (IOLs) in terms of their deviation from an ideal square as a follow-up of preliminary in vitro studies of experimental poly(methyl methacrylate) IOLs and commercially available foldable hydrophobic IOLs. SETTING: Berlin Eye Research Institute, Berlin, Germany. METHODS: Twenty-four designs of hydrophilic acrylic IOLs were used in this study. For each design, a +20.0 diopter (D) IOL and a +0.0 D IOL (or the lowest available plus dioptric power) were evaluated. The IOL edge was imaged under low-vacuum (0.7 torr), high-magnification scanning electron microscopy (SEM) using an environmental microscope and standardized technique. The photographs were imported to a digital computer program, and the area above the posterior-lateral edge, representing the deviation from a perfect square, was measured in square microns. RESULTS: Currently available hydrophilic acrylic IOLs labeled as square edged had an area of deviation from a perfect square ranging from 60.84 to 871.51 mu m(2) for the +20.0 D IOLs and from 35.52 to 826.55 mu m(2) for the low-diopter IOLs. Although some differences in edge finishing between the IOLs analyzed were observed, edge surfaces of hydrophilic acrylic IOLs appeared overall smooth under environmental SEM. CONCLUSIONS: Analysis of the microstructure of the optic edge of currently available square-edged hydrophilic acrylic IOLs showed a large variation of the deviation area from a perfect square.