Abstract
Purpose: :
To longitudinally follow the epithelial thickness profile changes after myopic LASIK over a 1-year follow-up period and determine when and how epithelial thickening occurs and when the epithelial thickness profile reaches stability.
Methods: :
Artemis very high-frequency digital ultrasound (ArcScan) scans were performed across the central 10-mm diameter of the cornea in a population of 24 eyes preoperatively and 1 day, 1 month, 3 months, 6 months and 12 months after myopic LASIK with the MEL80 excimer laser in a 6-mm ablation zone and VisuMax femtosecond laser (both Carl Zeiss Meditec). For each eye, epithelial thickness maps were compared point-by-point by calculating the difference and performing paired t-tests between time points, calculated for the 10-mm diameter, 0.1-mm step mapped data matrix. For each consecutive pair of time points, maps of the mean change in epithelial thickness and t-test p-value were calculated.
Results: :
The mean preoperative spherical equivalent was -3.40±1.63 D (range: -0.75 to -6.00 D). Overnight, there was a central 5-mm zone of epithelial thickening (1 to 2 µm, p<0.01), surrounded by an annulus of epithelial thinning (4 to 6 µm, p<0.01) extending to the 8-mm zone. Between 1 day and 1 month, the epithelium thickened within the 7-mm zone by up to 5 µm (p<0.01) in a lenticular pattern with greater central thickening and progressively less thickening centrifugally. Between 1 and 3 months, the epithelium continued to thicken in the central 7-mm zone by approximately 1 µm (p<0.01). Between 3 and 6 months and between 6 and 12 months, there were no statistically significant changes in epithelial thickness across the whole 10-mm diameter.
Conclusions: :
The epithelial thickness profile was found to change in a lenticular fashion, with more thickening centrally than peripherally. 20% of the total increase in central thickness occurred over night, a further 63% between 1 day and 1 month postop and the final 12% between 1 month and 3 months postop. The epithelial thickness profile was stable between 3, 6 and 12 month time points. These epithelial changes partially explain the regression seen after myopic LASIK in the first 3 months and agree with the common finding that refractive stability is generally attained after 3 months for low to moderate myopic LASIK.
Keywords: cornea: epithelium • refractive surgery: LASIK