Comparison of the effect of reducing the diameter of back optical zone diameter of CRT and VST designed orthokeratology lens in controlling myopia progression

AIM:To compare and analyze the effectiveness and safety of reducing the diameter of the back optical zone diameter(BOZD)of orthokeratology lens designed by CRT and VST in controlling the progression of myopia in children and adolescents.METHODS:Retrospective study. The study subjects were 400 myopia patients aged 8-16 years who were admitted to the orthokeratology fitting center of our hospital from June 2019 to May 2022, with 400 eyes(including right eye data analysis). The subjects were divided into CRT-S group(BOZD<6.0 mm), CRT group(BOZD=6.0 mm), VST-S group(BOZD<6.2 mm), VST group(BOZD=6.2 mm)according to the brand of orthokeratology lens and BOZD group, with 100 cases in each group. Uncorrected visual acuity(UCVA), corneal flat K value, axial length, spherical equivalent, and incidence of corneal injury were collected and analyzed at 1 d, 1 wk, 1 and 6 mo, 1 and 2 a, respectively.RESULTS:After wearing lenses for 1 d, the UCVA of the VST-S group improved the fastest, but after 1 wk, all groups reached a good UCVA, and there was no significant difference between groups. The corneal flat K value of the CRT-S group decreased the most after wearing lenses for 6 mo, and there was no significant difference in the corneal flat K value of all groups after 1 year of lens wearing. At each time point, the axial length growth decreased significantly after reducing the BOZD of the same brand of orthokeratology lens. At 6 mo, there was no significant difference in the axial length growth and defocus ring diameter between the CRT-S group and the VST-S group, but at 1 and 2 a, the VST-S group had significantly lower axial length growth and defocus ring diameter than the CRT-S group. The growth of the diopter sphere and spherical equivalent(SE)was significantly reduced when the BOZD of the same brand of orthokeratology lens was reduced at 2 a follow-up. The VST-S group had the smallest changes in the degree of SE and had the best myopia control effect. There was no significant difference in the change value of the diopter cylinder and the incidence of corneal injury among the four groups.CONCLUSION:Reducing the BOZD of the orthokeratology lens can effectively control the growth of the axial length and the progression of myopia degree. The myopia control effect of the VST lens is better than that of the CRT lens after reducing the BOZD. Reducing the BOZD of the orthokeratology lens does not increase the risk of additional corneal injury.