Threshold thickness of foveal outer nuclear layer associated with outcomes of photodynamic therapy in central serous chorioretinopathy.

OBJECTIVES To investigate the threshold thickness of the foveal outer nuclear layer (ONL) associated with favourable visual outcome after half-dose photodynamic therapy (PDT) in patients with central serous chorioretinopathy (CSC). METHODS The CSC patients were divided into two groups according to whether their best-corrected visual acuity (BCVA) at 1 year after half-dose PDT was 20/20 or worse than 20/20. Three multivariable logistic regression models were respectively created to determine the prognostic value of the pre-PDT foveal ONL thickness, the pre- and the post-PDT foveal ONL thickness ratio, which was defined as the foveal ONL thickness in the CSC eye to that in the normal contralateral eye, for predicting the outcome of half-dose PDT. The areas under the receiver operating characteristic curves (AUCs) were compared and the best cut-off values were determined, respectively. RESULTS Totally, 134 patients were included. The pre-PDT foveal ONL thickness, the pre-PDT and the post-PDT foveal ONL thickness ratios were all independent predictors of the outcome after half-dose PDT in their respective model (all P < 0.05). The AUC of the post-PDT foveal ONL thickness ratio was significantly higher than the AUCs of the other two parameters (0.940 vs 0.840 and 0.882, DeLong test: both P < 0.05), with the cut-off value of 0.81. CONCLUSIONS The threshold of the foveal ONL thickness ratio is 0.81. Active CSC eyes with a foveal ONL thickness ratio of 0.81 or more could probably retain BCVA of 20/20 after half-dose PDT. They were considered reasonable to wait for spontaneous resolution of sub-retinal fluid.