Comparison between the change in total corneal astigmatism and actual change in refractive astigmatism in transepithelial photorefractive keratectomy (tPRK), laser in situ keratomileusis (LASIK) and femtosecond laser assisted laser in situ keratomileusis (FsLASIK)

Purpose To compare changes in astigmatism by refraction and total corneal astigmatism after tPRK, LASIK and FsLASIK. Setting Specialty Eye Hospital Svjetlost, Zagreb, Croatia. Design Partially masked, semi-randomized, prospective, case-by-case, interventional, clinical study. Methods Patients with a stable refraction (-0.75DS to -8.00DS, astigmatism <= 1.00DC) underwent tPRK, LASIK or FsLASIK without complication. Astigmatism was measured at both corneal surfaces over the central 3.2 mm zone (approximately using Pentacam HRTM) preoperatively and 3 months postoperatively. Pentacam and refraction data were subjected to vector analysis to calculate the surgically induced changes in i) total corneal astigmatism (SIA(TCA)) ii) any astigmatism by refraction (SIA(R)) and the vectorial difference (DV) between SIA(TCA) and SIA(R.) Results Reporting key findings (p < .01), there was a significant difference between mean SIA(TCA) and SIA(R) powers after tPRK (75eyes) but not after LASIK (100eyes) or FsLASIK (100eyes). Mean (+/- sd,95% CIs) values for DV powers were, tPRK -1.13DC(+/- 0.71, -1.29 to -0.97), LASIK -0.39DC(+/- 0.23,-0.44 to -0.34), FsLASIK -0.55DC(+/- 0.38,-0.62 to -0.47). The differences were significant. For the tPRK and FsLASIK cases, linear regression revealed significant associations between I) SIA(TCA) (x) &DV (z) powers (tPRK z = 1.586x-0.179, r = 0.767, p < .01; FsLASIK z = 0.442x-0.303, r = .484,p < .01), II) sines of SIA(TCA) (x(1)) &DV (z(1)) axes (tPRK, z(1) = 0.523 x (1) + 0.394, r = .650,p < .01; FsLASIK z(1) = 0.460 x (1)-0.308, r = .465,p < .01). Conclusions tPRK is more prone to unintended changes in astigmatism. The difference between SIA(TCA) & SIA(R) after tPRK or FsLASIK is mediated by SIA(TCA). Photoablating deeper regions of the cornea reduces the gap between SIA(TCA) & SIA(R).