Abstract: Objective To study the changes in ocular surface before and after corneal collagen cross-linking in patients with keratoconus. Methods A retrospective study was conducted on 42 patients(60 eyes)diagnosed with keratoconus at the Ophthalmology Center of Hunan Provincial People's Hospital from November 2020 to May 2021 who met the inclusion and exclusion criteria and received high-energy accelerated corneal collagen cross-linking after providing informed consent. Based on corneal maximum curvature(Kmax), the patients were divided into the following three groups: mild, moderate, and severe. Further, the patients were divided into three groups according to the difference between flat keratometry(K1)and steep keratometry(K2), namely astigmatism: group A(0≤K2-K1≤2.5D), group B(2.5D < K2-K1≤5D), and group C(K2-K1>5D). The changes and characteristics of Kmax, K1, K2, corneal thickness, astigmatism, tear breakup time, tear meniscus height at 1 and 3 months before and after corneal collagen, and cross-linking were recorded. SPSS 26.0 software was used for statistical analysis to determine any difference in parameters at different time points before and after surgery. The test level was considered as α=0.05, and P<0.05 was considered statistically significant. Results For the Kmax group, preoperative baseline corneal thickness, K1, K2 showed statistical significance(P<0.001), whereas age, astigmatism, tear meniscus height, and tear breakup time did not(P=0.35、0.22、0.63、0.57). Significant differences were noted in corneal thickness, Kmax, tear meniscus height, K1, and K2 at different time points before and after surgery among the three groups(F_time=52.72, 5.22, 3.30, 5.06, 5.25, respectively, P<0.05; F_group=9.25,38.28,P<0.05,2.48,P>0.05,13.37,P<0.05,6.28,P>0.05). There were no significant differences in tear breakup time at different time points before and after surgery among the three groups(F_time=1.001,P=0.38;F_group=0.953,P=0.40). For the astigmatism group, preoperative baseline Kmax, K1, K2 were statistically significant(P=0.001、0.02、<0.001), whereas age, corneal thickness, tear meniscus height, and tear breakup time were not(P=0.13、0.43、0.96、0.11). Significant differences were noted in corneal thickness, Kmax, tear meniscus height, K1, and K2 at different time points before and after surgery among the three groups(F_time=45.91, 6.61, 4.06, 5.19, 8.4, P<0.05; F_group =0.53,0.6,0.75,1.19,P>0.05,7.63,P<0.05). There were no significant differences in tear breakup time among the three groups at different time points before and after surgery(F_time=1.103,P=0.34;F_group=1.121,P=0.34). Correlation analysis was conducted between the tear meniscus height and tear breakup time of ocular surface parameters and the values of corneal topography parameters Kmax, K1, K2 and astigmatism before, 1 and 3 months after surgery. The tear meniscus height was negatively correlated with astigmatism 3 months after surgery(P=0.04), while there was no correlation between the tear meniscus height and astigmatism before and 1 month after surgery(P=0.88、0.13). The tear break up time 1 month after operation was negatively correlated with astigmatism(P=0.03), but there was no correlation with astigmatism at other time points(P=0.13、0.29). Conclusion High-energy accelerated corneal collagen cross-linking has no adverse effect on tear film stability in the early stage; it can affect the amount of tear secretion and cause a slight decrease in the amount of tear secretion in the early stage. In the early stage of high-energy accelerated corneal collagen cross-linking, the amount of tear secretion decreased, especially in severe astigmatism.

Key words: High-energy accelerated corneal collagen cross-linking, Keratoconus, Ocular surface, Tear breakup time, Tear meniscus height