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.