Aims To investigate the lowest effective fluence rate of photodynamic therapy (PDT) for treating chronic central serous chorioretinopathy (CSC).

Methods Fifty-one eyes of 51 patients 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 (BCVA), central foveal thickness (CFT), subfoveal choroidal thickness (SFCT), integrity of the outer retinal layer and complications were evaluated at baseline and at the follow-up periods after PDT.

Results 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 (p=0.009), and 80.0%, 94.0% and 100.0%, respectively, at 12 months (p=0.06). The recurrence rate in the 50%-fluence group was lower than that in the 30%- and 40%-fluence groups at 12 months (30% vs 50%, 40% vs 50%; p=0.002, p=0.030, respectively (log-rank test)). The mean BCVA improved significantly 12 months after PDT only in the 40%- and 50%-fluence groups (p=0.005, p=0.003, respectively). Mean CFT and SFCT decreased significantly at 12 months in the three groups. The rate of complications did not differ significantly among the three groups.

Conclusions A 50%-fluence rate of PDT seems to be the most effective for treating chronic CSC, considering the low recurrence rate and high rate of complete SRF resolution, compared with other low-fluence PDT.

Trial registration number NCT01630863.