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

Purpose: To compare neodymium:YAG (Nd:YAG) laser effects on acrylic, silico ne, and poly(methyl methacrylate) (PMMA) intraocular lens (IOL) polymers. Methods: Ten Nd:YAG. laser exposures were produced in each of 6 implantatio n-quality acrylic (Alcon MA60BM), silicone (Staar AQ1016), and PMMA (Alcon MC60BM) IOLs under identical conditions. Each polymer type was irradiated a t 6 power settings (0.3, 0.5, 1.0, 1.5, 2.0, and 3.0 mJ) and at 2 local poi nts (midpoint of lens optic and on the posterior surface to which a celloph ane membrane was affixed). The linear extent of the damage was measured usi ng light microscopy. Specimens exposed to 1.0 mJ were processed for scannin g electron microscopy. Results: The damage threshold (greater than or equal to 5 mu m depth) was 0 .3 mJ for silicons and 1.0 mJ for acrylic and PMMA IOLs. At the clinically relevant power levels, 1.0 to 2.0 mJ, the depth of damage in the acrylic po lymer was 11.9 to 30.5 times less than the depth in the silicone polymer. S imilarly, the depth of damage in the PMMA polymer was 5.4 to 52.6 times les s than the depth in the silicone polymer. The morphologic pattern of damage in the silicone IOL showed a deep, irregularly configured trough with mean dering tendrils. Acrylic IOL damage morphology consisted of an ameboid-shap ed entry site without radiating fractures and mild posterior penetration. P oly(methyl methacrylate) IOL damage consisted of a shallow focal trough wit h radiating fractures. Conclusions: The silicone IOL polymer had the lowest threshold for laser-in duced damage and greater linear extension of damage than the PMMA and acryl ic IOL polymers. Poly(methyl methacrylate) and silicone polymers exhibited collateral damage or ejected particulates adjacent to the entry site, where as the acrylic polymer showed a discrete locus of damage.