Induced irregular astigmatism in hypermetropic PRK and LASIK: a bilateral cohort study

Abstract

Purpose: To determine if there was a difference in irregular astigmatism following hypermetropic correction with Photorefractive Keratectomy (PRK) and Laser In Situ Keratomileusis (LASIK) by Fourier analysis of corneal topographical data.Methods: Thirty‐six eyes of 18 patients affected by hypermetropia were enrolled as part of a prospective study in which one eye was treated with PRK and the other with LASIK. In the eyes that underwent LASIK the flap was cut on a nasal hinge with a LSK one microkeratome. The laser system was a Summit SVS Apex Plus with an optical zone of 6.5 mm and a blending zone of 1.5 mm. Corneal topographical data was acquired with a TMS‐1 pre‐operatively and at 1, 3, 6 and 12 months post‐operatively. The dioptric files for each time point were converted into ASCII format and subsequently analysed with purpose written software to extract the Fourier harmonics. This permitted the objective analysis of the irregular astigmatism, equivalent spherical component and regular astigmatism.Results: The irregular astigmatism increased in both groups post‐operatively, reached a peak at 3 months and then reduced over the next 9 months. There was no statistically significant difference between the two groups at any time point (p < 0.05 all cases). At 12 months the irregular astigmatism values for both groups remained above their pre‐operative levels.Conclusion: The irregular astigmatism analysed in this study showed no statistically significant difference between the PRK and the LASIK group throughout the follow‐up period. It appears that, from a corneal topographical point of view, the two procedures induce an equal amount of irregular astigmatism.