Regional and Temporal Changes in Choroidal Vascularity after Panretinal Photocoagulation in Diabetic Retinopathy: A Widefield SS-OCTA Study

Purpose: To investigate the changes in choroidal vasculature after panretinal photocoagulation (PRP) in patients with proliferative diabetic retinopathy (PDR) using widefield swept-source optical coherence tomography angiography (SS-OCTA). Methods: Thirty eyes of 30 PDR patients were enrolled and underwent SS-OCTA examination before PRP, and at 1 month and 3 months after PRP. Twenty-two age-matched healthy volunteers served as controls. Choroidal thickness (ChT), choroidal vascular volume (CVV), choroidal vascularity index (CVI), choroidal stromal volume (CSV), choriocapillaris flow deficit percentage (CC FD%), and central macular thickness (CMT) were automatically measured within concentric rings of 2.5, 5, 12, and 19 mm centered on the fovea. Results: Post-PRP choroidal changes showed distinct regional specificity and time dependence. In the periphery (12–19 mm): CVV decreased (-5.45% at 1 month, P =0.045; -8.23% at 3 months, P <0.001); CC FD% increased (+48.9% at 1 month, +80.7% at 3 months, both P <0.001); CVI decreased only at 3 months (-3.57%, P =0.011); CSV remained unchanged. In the central region (0–2.5 mm): except for a mild decrease in CVV at 3 months (-4.01%, P =0.009), all other parameters showed no significant changes. CMT progressively increased (+ 7.49 7.50% at 1 month, +12.32% at 3 months, both P <0.01). Exploratory analysis showed that central Δ CVV was independently positively correlated with Δ CMT ( β =0.219 P =0.002) Exploratory regression analysis showed that baseline CMT and central ΔCVV were independently associated with ΔCMT (β=0.352, P =0.041; B=528.414, P =0.002, respectively). Conclusion: PRP induces “vessel-first atrophy” in the periphery with relative central preservation, supporting hemodynamic redistribution. Widefield SS-OCTA effectively evaluates post-PRP choroidal changes. The association between central choroidal vascular volume change and macular edema requires further investigation.