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 microm(2) for the +20.0 D IOLs and from 35.52 to 826.55 microm(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.