To investigate long-term changes in subfoveal choroidal thickness (SCT) after photodynamic therapy (PDT) and their relationship with chronic central serous chorioretinopathy (CSC) recurrence.

Retrospective, observational, comparative case series.

Fifty-seven eyes with chronic CSC (52 patients, ≥2 years follow-up) treated with half-fluence or half-dose PDT were divided into 2 groups: those with incomplete CSC resolution or subretinal fluid (SRF) recurrence (SRF+) and those with complete SRF absorption without disease recurrence (SRF−). The SCT was measured using spectral-domain optical coherence tomography and relative SCT ratios (follow-up SCT: baseline SCT ratio) were compared between the 2 groups.

Mean follow-up period was 33.9 ± 9.9 months (range: 24–62 months). Four of 57 eyes (7%) had persistent SRF after PDT and 12 of 53 eyes (22.6%) had initial SRF resolution with SRF recurrence. The SRF+ group had a slower reduction in SCT during the first month (P < .001) and a higher relative SCT ratio than the SRF− group throughout follow-up (P < .001). The relative SCT ratio at 1 month was highly predictive of CSC recurrence (area under the curve = 0.902, 95% confidence interval: 0.823–0.982). Using a relative SCT ratio cutoff of 93.1%, sensitivity of this measure was 93.8% and specificity was 78.1%.

Those with incomplete SRF absorption or SRF recurrence had a slower SCT decline at 1 month and a higher SCT ratio throughout follow-up compared to those without CSC recurrence. The SCT changes may reflect PDT efficacy and help predict long-term recurrence and early treatment outcomes.