This paper reports on our progress using an erodible mask to perform Photorefractive Keratectomy (PRK) for the correction of myopic astigmatism. We describe modifications to the mask, the mask eye cup and the surgical microscope aimed at simplifying the procedure and improving the ergonomics of the hardware. We report the clinical results of the post-op exam for 20 patients who have undergone PRK for myopic astigmatism under a Phase hA study. At 6 months 60% of the eyes had a spherical equivalent within diopters (D) and 75% were within D. The residual cylinder was less than 1.0 D in 80% of the cases. The preoperative spherical equivalent manifest refraction ranged from -1.125 to -10.375 D (mean=-4.66 D) and the postoperative 6 month spherical equivalent ranged from +2.25 D to -2.75 D (mean=-O.37 D). The preoperative uncorrected visual acuity was 20/500 in 75% of the patients. The best preoperative uncorrected visual acuity was 20/80. The postoperative uncorrected visual acuity was better than 20/125 in 100% and better than 20/40 in 70% of the patients. The results compare favorably with an earlier Phase IIA study for performing PRK with a computer-controlled iris. Most important, the clinical data show the absence ofany significantcorneal haze and no significant decrease in spectacle corrected visual acuity. Although more long term follow-up is needed, the preliminary results supportthe safety and effectiveness ofusing an erodible mask to perform PRK for myopic astigmatism.
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