Abstract
Purpose: :
To examine long-term changes in corneal power and aberrations in patients randomized to PRK or LASIK.
Methods: :
Forty-five patients with myopia from -6 to -8 diopters (spherical equivalent refraction) were randomized to PRK (n = 20) or LASIK (n = 25). Patients were examined preoperatively and postoperatively at 1, 3, 6, and 12 months, and after 3 and 7 years. Investigations included topography (TMS-1, Tomey), ultrasound pachymetry (CCT), refraction, and pneumotonometry (IOP). Only patients that attended the seven-year control and had not been reoperated, were included in data-analysis (7 LASIK and 9 PRK patients). Topographical data were used to calculate corneal power and aberrations from Zernicke polynomial decomposition of the corneal wavefront.
Results: :
One month after surgery, corneal power was reduced similarly in PRK and LASIK treated eyes. During 1 year after PRK, corneal power increased significantly and remained stable from 1 to 7 years. In contrast, power changed only little the first year after LASIK, but continued to increase, with significant changes from 1 to 3, and 3 to 7 years. CCT increased significantly the first year after PRK, while no significant increase occurred after LASIK; still, changes in CCT were positively correlated with time after surgery. Both PRK and LASIK induced a significant increase in spherical aberration that remained constant for 7 years. PRK also caused an increase in coma that gradually decreased from 1 month to 7 years post surgery. No significant change in other higher order aberrations was observed after either surgical approach. Long-term changes in corneal power and aberrations were not correlated to changes in CCT, refraction, or apparent IOP.
Conclusions: :
Corneal biomechanical properties may not be stable even 7 years after LASIK, as indicated by the continuing increase in corneal power. In contrast, PRK appears stable from one year post- surgery. Apart from a gradual decrease in coma after PRK, no long-term changes in corneal higher order aberrations occur. Generalization of the present observations should be performed with caution due to the limited number of patients attending the seven year control.
Clinical Trial: :
www.clinicaltrials.gov NCT00404105
Keywords: refractive surgery: comparative studies • refractive surgery: corneal topography