A novel analysis of Scheimpflug total corneal refractive power following corneal cross-linking in mild to moderate keratoconus

AIM:To detect an earlier improvement in mild to moderate keratoconus following corneal cross-linking(CXL) with total corneal refractive power(TCRP) using ray tracing method.METHODS:A total of 40 eyes of 30 consecutive patients who underwent CXL for progressive keratoconus were retrospectively enrolled. The following keratometric parameters provided by Pentacam HR, including maximum keratometry(Kmax), steepest keratometry(Ksteep), 3 mm zonal TCRP centered over corneal apex(TCRPapex,zone 3 mm), zonal mean keratometry and TCRP centered over corneal cone(Kmcone,zone and TCRPcone,zone 1, 2, 3 mm) were evaluated preoperatively and 1, 3, 6, and 12 mo postoperatively. Groups 1 and 2 were defined based on Kmax at postoperative 1 mo as improved(the initial improvement group) or worsen(the initial deterioration group) compared to the preoperative level.RESULTS:In the overall group, only keratometric parameters based on ray tracing method displayed significant improvement early at 3 mo postoperatively, in which TCRPcone,zone 1 mm and 2 mm exhibited the largest flattening(0.57 D and 0.53 D,respectively). In Group 1, only Kmax, Kmcone,zone 2 mm and TCRPcone,zone 2 mm showed significant improvement initially at 1 mo postoperatively, in which Kmax exhibited the largest improvement(1.05 D), followed by TCRPcone,zone 2 mm(0.82 D). In Group 2, only keratometric parameters based on ray tracing method and Kmcone,zone 3 mm showed slight but not significant improvement early at 3 mo, in which TCRPcone,zone 3 mm displayed the most improvement(0.19 D), followed by TCRPcone,zone 2 mm(0.15 D).CONCLUSION:The findings indicate that a 2 mm zonal TCRP centered over Kmax could earlier detect keratometric improvement by CXL compared to other commonly used parameters in mild to moderate keratoconic eyes.