Dynamic changes of corneal lag and corneal resistance factor in children with different degrees of myopia

AIM: To investigate the dynamic changes of corneal hysteresis(CH)and corneal resistance factor(CRF)before and after orthokeratology(OK)in children with different degrees of myopia.METHODS: Totally 40 cases(80 eyes)of myopic children treated in our hospital from January 2019 to January 2020 were retrospectively analyzed. The subjects were divided into low-grade group and medium-grade group according to the spherical equivalent(SE)level. They were all treated with night wearing OK glasses. The LogMAR naked eye vision of the children was detected and recorded before and 1wk, 1, 6mo and 1a after wearing glasses. The levels of central corneal thickness(CCT)and axial length(AL)were monitored by ocular a-ultrasound, the SE level was measured by comprehensive optometry, the corneal curvature(K)was measured by corneal topography, the corneal compensated intraocular pressure(IOPcc)level was measured by ORA analyzer, and the values of CH and CRF were calculated at the same time.RESULTS:The naked visual acuity of LogMAR at 1wk, 1, 6mo and 1a after wearing glasses was significantly lower than that before wearing glasses(all P<0.05), and the SE and corneal curvature were significantly lower than that before wearing glasses(all P<0.05). CH and CRF at 1wk, 1, 6mo, 1a after wearing glasses were significantly lower than those before wearing glasses(all P<0.05). Compared with 1wk after wearing glasses, CH was significantly increased at 1, 6mo and 1a after wearing glasses(t=6.010, 6.447, 6.556, all P<0.05), CRF was significantly increased(t=6.429, 6.786, 7.143, all P<0.05). One week after wearing glasses, CH and CRF were positively correlated with K and CCT(P<0.05); 1mo after wearing glasses, CH and CRF were positively correlated with K and CCT(P<0.05). At 1wk, 1, 6mo and 1a after wearing glasses, CH in low degree group was significantly lower than that before wearing glasses(t=8.330, 3.922, 3.432 and 3.334, all P<0.05), and CH in moderate degree group was significantly lower than that before wearing glasses(t=13.276, 4.964, 4.052 and 4.387, all P<0.05). Compared with 1wk after wearing glasses, CH in low-grade group was significantly higher(t=4.413, 4.903, 5.001, all P<0.05)and in moderate group was significantly higher(t=8.312, 8.773, 8.889, all P<0.05)at 1, 6mo and 1a after wearing glasses. One week after wearing glasses, the CH level of moderate group was significantly lower than that of low group(t=2.089, P<0.05). CRF in low-grade group was significantly lower than that before wearing glasses(t=8.684, 3.928, 3.618, 3.308, all P<0.05), CRF in moderate group was significantly lower than that before wearing glasses(t=15.432, 5.576, 5.057, 4.668, all P<0.05), CRF in low-grade group was significantly higher than that after wearing glasses(t=4.755, 5.065, 5.376, all P<0.05), and CRF in moderate group was significantly higher than that after wearing glasses(t=9.856, 10.374, 10.764, all P<0.05). One week after wearing glasses, the CRF level of moderate group was significantly lower than that of low group(t=2.610, P