Experimental neodymium:YAG laser damage to acrylic, poly(methyl methacrylate), and silicone intraocular lens materials

Abstract

Purpose: To compare neodymium: YAG (Nd:YAG) laser effects on acrylic, silicone and poly(methyl methacrylate) (PMMA) intraocular lens (IOL) polymers Methods: Ten Nd: YAG laser exposures were produced in each of 6 implantation quality acrylic (Alcon MA60BM), silicone (Staar AQ1016), and PMMA (Alcon MC60BM) IOLs under identical conditions. Each polymer type was irradiated at 6 power settings (0.3, 0.5, 1.0, 1.5, 2.0, and 3.0 mJ) and at 2 focal points (midpoint of lens optic and on the posterior surface to which a cellophane membrane was affixed). The linear extent of the damage was measured using light microscopy,. Specimens exposed to 1.0 mJ were processed for scanning electron microscopy. Results: The damage threshold (≥ μm depth) was 0.3 mJ for silicone and 10 mJ for acrylic and PMMA IOLs. At the clinically relevant power levels, 10 to 20 mJ the depth of damage in the acrylic polymer was 11.9 to 30.5 times less than the depth in the silicone polymer. Similarly, the depth of damage in the PMMA polymer was 5.4 to 52.6 times less than the depth in the silicone polymer. The morphologic pattern of damage in the silicone IOL showed a deep, irregularly configured trough with meandering tendrils. Acrylic IOL damage morphology consisted of an ameboid-shaped entry site without radiating fracture and mild posterior penetration. Poly(methyl methacrylate) IOL damage consisted of a shallow focal trough with radiating fractures. Conclusions: The silicone IOL polymer had the lowest threshold for laser-induced damage and greater linear extension of damage than the PMMA and acrylic IOL polymers. Poly(methyl methacrylate) and silicone polymers exhibited collateral damage or ejected particulates adjacent to the entry site, whereas the acrylic polymer showed a discrete locus of damage.