DAMAGE IN VARIOUS INTRAOCULAR LENSES BY N EODYMIUM-YAG LASER PHOTODISRUPTION

Background Neodymium:YAG laser capsulotomy frequently damages the intr aocular lens (IOL). This damage, mainly caused by acoustic shock wave and thermal conduction,results in opacities in the IOL, which may caus e glare or image degradation. Because of the introduction of new IOL m aterials in cataract surgery, investigation of YAG laser resistance of these IOL materials seems to be necessary. Materials and methods A to tal of 17 standard IOLs of different types and classes of materials we re tested as follows: Class I: Acrylate a) PMMA, compression molding, b) PMMA, compression molding, heparin-surface modified, c) acrylate/me thacrylate copolymer; Class II: Silicone: a) Polydimethylsiloxane, b) Polydimethyldiphenylsiloxane; Class III: Hydrogel: a) poly-hydroxyethy lmethacrylate (poly-HEMA): b) polyacrylate-hydrogel; Class IV: Thermos et polymer: methylmethacrylate, hydroxyethylmethacrylate, ethylene gly col dimethacrylate. Each IOL was placed in a rectangular trans parent acrylic test chamber filled with balanced salt solution and subjected to irradiation from a Q-switched Nd:YAG laser. The laser beam was focu sed on the posterior surface and inside of the IOLs. The optic of the IOL was divided into four target zones and each zone was subjected to 40 bursts inside the lens and 40 bursts on the posterior surface of th e lens. Laser power settings were: 1.1 mJ, 1.1 mJ with 0.4 mm defocus, 2.1 mJ and 4 mJ and one burst was applied (wave length 1064 nm, funda mental mode, duration 7+/-2 nanoseconds, spot size 15 mu m in air). Fo llowing exposure, each lens was examined by light microscopy for the i nterior damage and by scanning electron microscopy fdr the posterior s urface damage. For quantitative analysis, the extent of each superfici al damage was evaluated by an image analysis system using at least ori ginal magnification x 1400. Results Each IOL material demonstrated spe cific morphologic damage patterns. Intralenticular damage: Class I: cr acks with radiating fractures with smaller extent in group Ic; Class I I: blistered snowball-like inclusions; Class III: localized small hole s; exception: IIIb: with very short radiating fractures; Class IV: ste llar pits with short radiating fractures. For silicone superficial pos terior damage sites a splash crater pattern with irregular melted edge s was observed, while acrylate damage sites demonstrated a melted or s tellate crater pattern with slightly raised edges. The silicone, poly- HEMA and the acrylic IOLs containing HEMA presented highest YAG laser resistance with the smallest amount of posterior damage in comparison to PMMA-IOLs. There was no marked increase in damage size in these IOL materials with higher energy exposure in this set-up. Conclusion For each material consistent and characteristic specific morphologic damag e patterns were observed. Foldable optic materials were more resistant against Nd:YAG-laser photodisruption than rigid optic materials. Indi vidual laser strategies for each IOL-material and design should be ded ucted.