OPTICAL PROFILOMETRY OF POLY(METHYLMETHACRYLATE) SURFACES AFTER RESHAPING WITH A SCANNING PHOTOREFRACTIVE KERATECTOMY (SPRK) SYSTEM

A prototype frequency-quintupled Nd:YAG laser was used with a scanning system to create, on poly(methylmethacrylate)(PMMA) blocks, ablations corresponding to a correction of 6 diopters of myopia by photorefract ive keratectomy. The topography of the ablated samples was measured wi th an optical profilometer to evaluate the smoothness and accuracy of the ablations. The ablation depth was larger than expected. With a 50% to 70% spot overlap, large valley like variations with a maximum peak -to-peak amplitude of 20 mu m were observed. With an 80% spot overlap, the rms surface roughness was 1.3 mu m and the central flattening was 7 diopters. This study shows that optical profilometry can be used to determine precisely the ablation per pulse and the smoothness and acc uracy of surface ablations. Knowing the exact ablation per pulse is ne cessary to produce a smooth and accurate corneal surface by scanning p hotorefractive keratectomy. (C) 1996 Optical Society of America.