Co-localized OCT and diffuse reflectance spectroscopy in a fiber-optic probe for dosimetry in retinal endolaser photocoagulation

Retinal endolaser photocoagulation (REPC) is a widely performed vitreoretinal procedure, yet quantitative intraoperative treatment outcome assessment remains challenging using conventional operating microscopes or microscope-integrated optical coherence tomography (miOCT) systems. In this work, we present a dual-fiber 21G endolaser probe with instrument-integrated optical coherence tomography (iiOCT) and diffuse reflectance spectroscopy (DRS) via a monolithic 3D nano-printed sensor head for co-localized laser delivery and multimodal sensing. Phase-sensitive iiOCT M-scans (consecutive A-scans acquired over time) monitor structural tissue alterations during laser irradiation, while broadband illumination and collection via a dual-clad fiber and multi-mode fiber capture pre- and post-operative diffuse reflectance spectra. Using ex vivo porcine eyes, sensor-derived metrics were evaluated against microscopic lesion visibility grades and miOCT-measured lesion diameters using mixed-effects models under leave-one-eye-out cross-validation. Both single-sensor channels improved predictive performance over laser parameters alone. For ordinal lesion visibility classification, the DRS-derived spectral tilt increased overall accuracy from 0.784 to 0.867 and the correct classification rate for barely visible lesions from 38.1% to 66.7%. For lesion diameter prediction, the iiOCT-derived metric achieved the best single-sensor performance, increasing mean R² by 5.7 percentage points to 0.776. Combining structural and spectral metrics yielded the highest performance for both tasks, with a visibility accuracy of 0.869 and a diameter-prediction R² of 0.790. These results demonstrate the feasibility of co-localized multimodal sensing in a single fiber-optic probe and provide a foundation for future real-time, sensor-guided endolaser surgery.