Fourier analysis of induced irregular astigmatism. Photorefractive keratectomy versus laser in situ keratomileusis in a bilateral cohort of hyperopic patients

J Cataract Refract Surg. 2003 Sep;29(9):1709-17. doi: 10.1016/s0886-3350(03)00524-8.


Purpose: To analyze corneal topographic data by Fourier analysis to determine differences in irregular astigmatism following spherical hyperopic correction by photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK).

Setting: Department of Ophthalmology, St. Thomas' Hospital, London, United Kingdom.

Methods: Thirty-six eyes of 18 patients with moderate hyperopia had LASIK in 1 eye and PRK in the other eye. The flap was cut on a nasal hinge with a Moria LSK One microkeratome. The laser was a Summit SVS Apex Plus with an optical zone of 6.5 mm and a blending zone of 1.5 mm. Corneal topographic data were acquired with a TMS-1 topographer (Computed Anatomy Inc.) preoperatively and 1, 3, 6, and 12 months postoperatively. The ASCII files containing the dioptric power values were extracted and analyzed with custom-written software to extract the Fourier harmonics.

Results: The irregular astigmatism increased in both groups postoperatively, peaking at 3 months and then decreasing over the next 9 months. There was no statistically significant difference between the 2 groups at any time point (P<.05). The change in the topographically derived equivalent sphere showed undercorrection in both groups at all time points. Regular astigmatism showed a marginal statistically significant increase in the LASIK group at 12 months (P =.049).

Conclusion: Irregular astigmatism, equivalent sphere, and regular astigmatism were not significantly different in the PRK and LASIK groups during the follow-up. Based on the corneal topography, the 2 procedures induced an equal amount of irregular astigmatism.

Publication types

  • Comparative Study

MeSH terms

  • Adult
  • Astigmatism / pathology
  • Astigmatism / physiopathology*
  • Cohort Studies
  • Corneal Topography
  • Female
  • Follow-Up Studies
  • Fourier Analysis*
  • Humans
  • Hyperopia / surgery*
  • Keratomileusis, Laser In Situ*
  • Lasers, Excimer
  • Male
  • Middle Aged
  • Models, Biological
  • Photorefractive Keratectomy*
  • Postoperative Period