Dynamic Observation Of Corneal Confocal Microscopy In Vivo After TransPRK

Objective: To observe the morphological changes of cells and nerve fibers in different layers of corneas after Trans PRK by in vivo confocal microscopy(IVCM)and the changes of nerve fibers in different layers of corneas after Excimer laser.Methods: A prospective study was conducted.Continuous confocal microscopy was used to observe the corneal surface of Trans PRK patients before and after operation.A total of 103 patients(204 eyes)with mild to moderate Myopia who underwent Trans PRK in the refractive center of Dalian Third People's Hospital from November2018 to May 2019 were followed up for at least half a year.Eye Examination was performed according to the procedure before operation.UCVA and slit-lamp examination were performed 1 week,1 month,3 months and 6 months postoperatively.Laser scanning confocal microscopy was used to observe the corneal structures in the ablation area before and after surgery.The acquisition image was processed by ACCMetrics software.All the observation indexes were analyzed,and repeated measures were used to analyze the variance.The LSD-t Test was used to compare the differences between the divided groups..Results: UCVA reached preoperative BCVA in all cases at 6 months postoperatively.There were significant differences in the thickness of corneal epithelium between 3months and 6 months after operation(All p<0.05),and there was a continuous and linear structure of subbasal nerve in Central District cornea before operation,see H or Z bifurcation,moderate density.The transected end of corneal nerve could be seen at the subepithelial cutting interface at 1 week postoperatively.In 166 eyes,81.4% of the cornea of Central District showed thin filamentous nerve fibers with weak growth,partial discontinuity and no obvious bifurcation.At this time,the nerve density and other parameters were the lowest.In 185 eyes,90.7% nerve fibers were lengthened and gradually enlarged,and a few filamentous branches were seen at the end 1 month after operation.In 192 eyes(94.1%),the thickened long nerve fibers and filamentous nerve fibers were observed in 192 eyes(94.1%)and 199 eyes(97.5%)in 6 months postoperatively.After 1 week,1 month,3 months and 6 months,the corneal nerve recovered slowly and the parameters were increased.There were significant differences between pre-operation and post-operation(All p<0.05).At 6 months after operation,the indexes of subcutaneous nerve fibers were lower than before operation,and the morphology did not return to the pre-operation state.The corneal nerve recovered slowly,the density decreased and the curvature increased compared with that before operation.The anterior corneal Stroma cells were partially activated and the morphology of the cells was changed at the ablation site.The number of activated stromal cells decreased gradually with time.There were significant differences in the density of corneal stromal cells before and after Operation(p = 0.012),and the density of corneal stromal cells decreased significantly one week after operation,there was a significant difference between the two groups(p = 0.004).The density of stromal cells increased slowly 1 month,3 months to 6 months after operation.There was no significant difference between the three groups(All p > 0.05),but significant differences between the three groups before and after operation(All p<0.05).There was no significant difference of corneal deep stromal cell density between pre-operation and post-operation(p = 0.674).There was no significant difference in the parameters of endothelial cells before and after operation(All p > 0.05).Conclusion: Trans PRK is an optimal surface layer surgery with rapid visual acuity recovery and few postoperative adverse reactions.But confocal microscopy showed that it can still damage the corneal stroma cells and nerve fibers.Laser in Vivo confocal microscopy can be used to dynamically track the changes of corneal cells at any time.It can provide clues for the evaluation of visual quality and the prediction of postoperative complications such as Haze and dry eye.