The changes in corneal biomechanical parameters after phototherapeutic keratectomy in eyes with granular corneal dystrophy.

Purpose: To assess corneal biomechanical changes in eyes undergoing phototherapeutic keratectomy (PTK) and to investigate the relationship of PTK with corneal thickness.

Methods: We examined 36 eyes of 23 patients undergoing PTK for the treatment of granular corneal dystrophy (GCD). Corneal hysteresis (CH) and corneal resistance factor (CRF) were measured with an Ocular Response Analyzer before and 3 months after surgery. We also investigated the relationships between corneal biomechanical parameters and central corneal thickness before and after surgery.

Results: The CH was significantly decreased from 10.2+/-2.2 to 8.7+/-1.8 mm Hg after PTK (Wilcoxon signed-rank test, P<0.001), as was the CRF, from 10.3+/-2.0 to 8.5+/-1.8 mm Hg (P<0.001). We found a significant correlation between both CH and CRF and the central corneal thickness before surgery (Pearson correlation coefficient r=0.37, P=0.03 for CH, r=0.51, P=0.002 for CRF) and 3 months after surgery (r=0.54, P=0.001 for CH, r=0.74, P<0.001 for CRF).

Conclusions: PTK induces a significant decrease in the biomechanical parameters of the cornea. The corneal thickness may play some role in corneal biomechanics even in eyes with GCD.