Photorefractive keratectomy for myopia: single vs double-zone treatment in 166 eyes

We studied 58 single-zone and 58 double-zone treatments; attempted correction ranged between 6.50 and 10.00 D. There were no significant differences in the age or sex in the two groups. All the eyes received the same topical corticosteroid therapy. Refractive outcome showed a greater overcorrection in the double-zone than in the single-zone treatments, but the difference was not statistically significant (F = 3.17, p = 0.07). The refractive error shifted toward myopia significantly over time (F = 561.34, p < 0.0001). In the first-, third- and sixth-month follow up, the mean refractive error was +2.39 (+/- SD) +/- 1.94, +0.45 +/- 1.54, and -0.60 +/- 1.50 D in the single-zone treatments, while in the double-zone ones they were +1.95 +/- 2.49, +0.87 +/- 2.85 and +1.34 +/- 2.57 D, respectively. The Student's T test demonstrated a statistically significant difference of refractive outcome between the two groups only at 6 months (T = -3.788, p < 0.0001). Corneal haze decreased during follow up (F = 123.38, p < 0.0001) and was more severe in the single-zone than in the double-zone treatments (F = 9.28, p = 0.002). The Student's T test showed a significant difference at 6 months (T = 2.877, p = 0.006). The double-zone procedure appeared to be safer than the single-zone, but a longer follow up period and a greater number of treatments are required to draw final conclusions.