PurposeTo determine which subgroup of children would best benefit from 0.01% atropine eyedrop.MethodsThis post hoc secondary analysis assessed 68 subjects. Placebo for the first year and 0.01% atropine eye drops for the second year. According to the annual spherical equivalent progression (SEP) during the first year, subjects were subdivided into three groups: slow, moderate and fast (annual SEP > −0.50 D, −1.00 D < annual SEP ≤ −0.50 D, annual SEP ≤ −1.00 D, respectively).ResultsAfter 1 year of 0.01% atropine treatment, SEP was −0.37 ± 0.23 D, −0.57 ± 0.38 D, and −0.68 ± 0.49 D in the slow, moderate, and fast progression groups (P = 0.17). The group with faster SEP during the first year still showed faster SEP after treatment. The reduction of SEP (SEP of the second year minus SEP of the first year) in the moderate group was more than that in the slow group (0.22 ± 0.37 D vs. −0.10 ± 0.21 D, P = 0.007); the fast group was more than that in the slow group (0.57 ± 0.55 D vs. −0.10 ± 0.21 D, P < 0.001) and the moderate group (0.57 ± 0.55 D vs. 0.22 ± 0.37 D, P = 0.02). Faster SEP before treatment is related to the reduction efficiency (β = −0.5, P = 0.01).ConclusionFaster SEP before treatment is associated with a better treatment response to 0.01% atropine eye drops, with greater reduction in SEP after treatment. However, no significant association was found between baseline progression and axial elongation changes. Children with slow SEP cannot get significant myopia control benefit from 1-year 0.01% atropine treatment.Clinical Trial Registrationclinicaltrials.gov, identifier ChiCTR-IOR-17013898.