Effect Of Ablation Depth On The Endothelial Status In Eyes Undergoing Laser Assisted Transepithelial Photorefractive Keratectomy Of Saudi Myopic Patients.

To correlate ablation depth on corneal endothelial cell indices following transepithelial Photorefractive keratectomy (TPRK) in Saudi myopic patients. Also to present the correleation of ablation parameters to endothelial indices before at week 1 and week 12 follow-up of myopic eyes treated with TPRK and factors affecting the correlation of ablation parameters to the changes in endothelial cell count after TPRK.

This study included adult myopic patients aged 18 years or older with BCVA 0.0 LogMAR, likely to have a residual stromal bed of >350 μm at the thinnest location on the cornea, and without dry eye who underwent T-PRK at a private ophthalmology center in Saudi Arabia between January 2022 and December 2022.

This was a cohort study of myopic eyes treated with TPRK.  The corneal endothelial cell-related indices were generated by using non-contact specular microscopy (Tomey, EM-3000, Japan). The mode of this assessment was non-contact, auto-alignment. Central fixation and auto-measurement with Trace method. Of the 16 images captured automatically, the best endothelial image was taken for the analysis. The changes in endothelial cell (EC) density and other indices were noted one week (W1) and 12 weeks (W12) after TPRK was the main outcome. The laser ablation depth (AD) was correlated to the EC indices. The preoperative factors were also correlated to the outcomes using regression analysis to review predictors of change in the EC density.

We had 120 eyes of 60 myopic patients operated on for TPRK. The mean of ADmaximum (ADm) and central ADcentral (ADC) were 110.3 ± 23.7 µ and 108.8 ± 24.4 µ respectively. The median of change in EC count at W1 and W12 were -9.5 (interquartile range IQR -33.0; 17.0) and -3.0 (IQR -29.3; 13.3) respectively. The ADm was negatively correlated to a change in EC density at W1 (Wilcoxon Z =-2.7, P = 0.006) and at W12 (Z = -3.74, P <0.001). ADm (Kruskal Wallis test P = 0.167) ADc (K-W P = 0.08), Central Corneal Thickness (K-W P = 0.65) and use of mitomycin-C (K-W P = 0.357) were not significant predictors of the change in EC density at W1. None of the variables were significant predictors of the change in EC density at W12. 

The variation in endothelial cell indices at one week and 12 weeks after TPRK compared to those before surgery was wide. The ablation depth by excimer laser used in TPRK although influences some of the changes in indices related to the endothelial cell status after surgery, could not be a predictor. Preoperative refractive status and the central corneal thickness could determine ablation depth and should be accounted for before concluding about tole of ablation depth influence on endothelial cell-related indices after TRPK.