AIM: To compare the progression of myopia in children wearing orthokeratology lenses combined with low-concentration atropine before and after drug withdrawal, to determine the rebound effect of drug withdrawal in orthokeratology lens wearers, and to analyze its causes based on changes in pupil diameter.METHODS:A prospective case-control study was conducted to collect 80 children with myopia who were treated with orthokeratology lenses combined with 0.01% atropine ophthalmic gel at the Xi'an No.1 Hospital from January to June 2022. One year later, they were divided into a drug withdrawal group(Group A, 40 cases)and a continuous medication group(Group B, 40 cases)based on whether they stopped taking the medication. The progression of myopia before and after drug withdrawal was observed by analyzing changes in axial length(AL)and spherical equivalent(SE)in the group A within 1 a before and after drug withdrawal. The changes in AL, pupil diameter(PD), and SE were compared between the group A and group B within 2 a, and the correlation between PD and AL growth was analyzed.RESULTS:In the group A, the AL increased by 0.17±0.23 and 0.29±0.18 mm at 0.5 and 1 a after drug withdrawal, respectively, which were both greater than before drug withdrawal(t=5.318, 2.983, both P<0.001). There was no statistically significant difference in SE growth between the two time points(P>0.05). There were no statistically significant differences in AL and PD between the group A and group B at baseline, 0.5 and 1 a during combined medication(all P>0.05). At 1.5 a, the AL growth of the group A was greater than that of the group B(0.32±0.27 mm vs 0.26±0.20 mm, t=7.363, P<0.001), and the PD was smaller than that of the group B(3.60±1.25 mm vs 4.12±1.92 mm, t=-7.541, P<0.001). At 2 a, the AL growth of the group A was greater than that of the group B(0.44±0.18 mm vs 0.32±0.14 mm, t=5.709, P<0.001), and the PD was smaller than that of the group B(3.67±1.31 mm vs 4.02±1.67 mm, t=-4.281, P<0.001). Correlation analysis showed a negative correlation between PD and AL growth at 0.5 and 1 a follow-ups over 2 a(R2=-0.156, -0.190, both P<0.001).CONCLUSION: After stopping low-concentration atropine in children wearing orthokeratology lenses, AL increased more rapidly than before drug withdrawal, PD decreased, and SE changed little. Compared with continuous medication, discontinuation of medication led to faster progression of AL with little change in diopter, and the larger the PD during orthokeratology lens wear, the slower the progression of AL.