Longitudinal polarization diversity optical coherence tomography before and after photodynamic therapy in chronic...

Central serous chorioretinopathy (CSC) is the fourth most common retinopathy globally. Chronic central serous chorioretinopathy (cCSC) is a subtype of CSC characterized by persistent or recurrent subretinal fluid (SRF) for more than 3 months. CSC's pathophysiology is described by choriocapillaries (CC) hyperpermeability and vascular congestion. Photodynamic therapy (PDT) is the current treatment of choice for cCSC. PDT causes vascular remodelling by inducing reactive oxygen species (ROS). Melanin in the retinal pigment epithelium (RPE) is a major target of ROS and can be observed non-invasively using polarization-diversity OCT (PD-OCT). Fourier-domain mode-locked (FDML) OCT is an imaging modality that can be used for high-resolution imaging of choriocapillaries.Our study aimed to evaluate melanin-related depolarization and CC changes longitudinally before and after PDT in patients with cCSC.

This prospective clinical pilot study was conducted in accordance with the Declaration of Helsinki and approved by the institutional review board (REB H15-02914). 5 eyes with cCSC were imaged at baseline and within one hour, one week, and one month after half-dose PDT. Eligible patients had cCSC with active disease on multimodal imaging and no other major ocular comorbidities. Imaging included custom-built swept-source OCT angiography (OCTA) and polarization-diversity OCT (PD-OCT) and commercial SSOCT. PD-OCT depolarization was qualitatively assessed using degree of polarization uniformity (DOPU). PD-OCT volumes were manually segmented into: (1) the RPE layer (Inner RPE to outer Bruch's membrane), the full choroidal slab (Outer RPE to Choroidoscleral interface).

PD-OCT revealed a decrease in DOPU after PDT across all patients. Manual segmentation of PD-OCT images showed that this effect was most prominent within the RPE-Bruch's Complex. The full choroidal slab demonstrated less depolarization post-PDT. FDML OCTA demonstrated transient flow alterations in the choriocapillaris within the same 4,000-µm PDT treatment zone. Immediately after PDT, FDML revealed irregular flow deficits and heterogeneous darkening across the choriocapillaris.

DOPU provides a novel, non-invasive marker for assessing RPE melanin integrity and may serve as a complementary tool for DOPU related changed following PDT in CSC. Our findings suggest a novel mechanism and transient effect of PDT action on RPE melanin.