Objective To investigate anterior segment variations under miotic and mydriasic conditions in patients with a posterior chamber implantabble collamer lens (ICL).Methods Ten patients (19 eyes) who underwent ICL implantation surgery at least two weeks prior were enrolled randomly in this self-controlled study.One percent pilocarpine or compound tropicamidc was administered to induce miosis or mydriasis,simulating responses to bright light or dark condifions.Parameters of the anterior segment under normal light conditions without eye drops,and with miosis and mydriasis were measured with anterier segment-optical coherence tomography,including anterior chamber depth (ACD),ICL vaulting and the white-to-white (WTW) distance.A paired t test was used to analyze the data.Results ACI) was 3.61±0.20 mm under normal conditions,3.42±0.15 mm under miosis and 3.64 ±0.22 mm under mydriasis.ACD in miosis was significantly shallower than under normal conditions (t=7.89,P＜0.01),while there was no difference between ACD in mydriasis and normal conditions.Vaulting was 0.61±0.14 mm under normal conditions,0.41±0.10 mm in miosis and 0.64±0.14 mm in mydriasis.Vaulting in miosis was significautly narrower than under normal conditions (t=10.51,P＜0.01),while there was no difference between vaulling in mydriasis and normal conditions.WTW distance was 11.40±0.28 mm under normal conditions,11.38±0.32 mm in miosis and 11.35±0.30 mm in mydriasis.There was no difference between WTW in miosis,mydriasis or normal conditions.Conclusion The anterior segment variations of patients with ICL under miosis or mydriasis stayed within a safe range.