Park DG, Jeong S, Noh D, et al. - In the present study, the researchers sought to examine the lowest effective fluence rate of photodynamic therapy (PDT) for treating chronic central serous chorioretinopathy (CSC). Fifty-one patients (51 eyes) with chronic CSC were randomly treated with 30% (n = 15), 40% (n = 16) or 50% (n = 17) of the standard-fluence rate of PDT and followed up for 12 months. The success rate, recurrence rate, mean best-corrected visual acuity, central foveal thickness, subfoveal choroidal thickness, the integrity of the outer retinal layer and complications have been assessed at baseline and at the follow-up periods after PDT. Data reported that the rate of complete subretinal fluid (SRF) resolution in the 30%-fluence, 40%-fluence and 50%-fluence groups was 60.0%, 81.2% and 100.0%, respectively, at 3 months, and 80.0%, 94.0% and 100.0%, respectively, at 12 months. Considering the low recurrence rate and high rate of complete SRF resolution compared with other low-fluence PDT, a 50%-fluence rate of PDT appears to be the most effective for treating chronic CSC.