Photorefractive keratectomy (PRK) with variable optical zone diameters for the correction of compound myopic astigmatism

Purpose. To determine whether the use of different optical zone (OZ) diameters for the astigmatic and spherical components of compound myopic astigmatism improves predictability and stability of refraction after PRK. Methods. Thirty-five eyes with myopia ranging from -3.50D to -13.00D (mean -7.90D; SD 2.40D) and astigmatism from -2.ODD to -5.00D (mean -3.00D±0.90D) were treated. The cylinder was corrected first, using a 5.5 to 6.5-mm OZ (corresponding to the videokeratographic extension of the astigmatic bow tie). A transition zone of at least 1.5 mm was added. The myopia was then corrected with an OZ of 5.5 to 6.5 mm. A Nidek EC 5000 excimer laser was used. Minimum follow-up was 12 months. Results. At 12 months postoperatively, the mean sphere was -0.06D±1.09D and the mean cylinder -0.22D±0.86D, with 83% of the eyes within 1.00D of attempted spherical correction, and 78% within 1.00D of attempted cylinder correction. Mean UCVA (decimal scale) improved from 0.02±0.01 to 0.56±0.27. No eye lost 2 or more lines of BCVA. Conclusions. This strategy for correcting myopic astigmatism appears to reduce the risk for regression and BCVA loss seen with other methods, probably because of the more effective correction of large-diameter astigmatic bow-tie patterns.