CORRECTION OF MYOPIA AND ASTIGMATISM USING AN ABLATABLE MASK

BACKGROUND: Most excimer laser refractive procedures use a computer dr iven mechanical diaphragm to shape the laser beam. Studies are current ly underway using an ablatable polymethylmethacrylate (PMMA) mask to t ransfer a new spherical or toric curve to the cornea for the correctio n of myopia and astigmatism; it may leave a smoother corneal surface t han diaphragm procedures. METHODS: As part of a Phase IIb FDA clinical study, 25 eyes of 25 patients underwent excimer laser photorefractive keratectomy using a hand held ablatable mask. Fifteen eyes had attemp ted spherical corrections of up to 6.00 diopters (D) and 10 had toric corrections of up to 6.00 D of sphere and 2.75 D of astigmatism. RESUL TS: Seventy-four percent of all eyes achieved uncorrected visual acuit y of 20/40 or better -86% in the spherical group and 63% in the astigm atism group. Sixty-nine percent of eyes were within +/- 1 D of the att empted correction. In eyes treated for astigmatism, mean astigmatism d ecreased from 1.48 D preoperatively to 0.86 D postoperatively. Approxi mately one half of the eyes treated for astigmatism had a decrease in cylinder of more than 0.5 D. One eye lost 2 Snellen lines of best sphe rical corrected visual acuity. Video keratography showed toric ablatio ns to result in an elliptical optical zone. Analysis of centration of the procedure showed 66% of ablations centered within 1.0 mm of the ce nter of the pupil aperture. CONCLUSIONS: The ablatable mask represents a promising modality for the treatment of eyes with both myopia and m yopic astigmatism.