Orientation-based evaluation of scleral collagen fibers in uveitic secondary glaucoma

PURPOSE: To compare scleral fiber orientation in eyes undergoing trabeculectomy between those with primary open-angle glaucoma (POAG) and uveitic secondary glaucoma (UG). METHODS: Twenty-nine eyes (17 POAG and 12 UG) that underwent trabeculectomy, during which scleral flaps were excised, were included. Cryosections (meridional cross-sections) were prepared from the excised scleral flaps and stained with either collagen type I (COLI) or α-smooth muscle actin (αSMA). Images were obtained by confocal fluorescence microscopy. Local two-dimensional fiber orientations were quantified using OrientationJ, with coherency (an index of local structural anisotropy) and energy (an index reflecting the magnitude of orientation information) as outcome variables. These parameters were compared between the POAG and UG groups. RESULTS: In COLI-stained samples, mean coherency values were 0.111 ± 0.092 in POAG and 0.127 ± 0.085 in UG (p < 0.001), while in αSMA-stained samples, the values were 0.163 ± 0.132 in POAG and 0.195 ± 0.138 in UG (p < 0.001), respectively. For energy, mean values were 0.276 ± 0.175 in POAG and 0.358 ± 0.194 in UG for COLI-stained sections (p < 0.001), and 0.429 ± 0.209 in POAG and 0.471 ± 0.203 in UG for αSMA-stained sections, respectively (p < 0.001). CONCLUSION: Scleral flaps excised during trabeculectomy in UG eyes exhibited significantly higher coherency, indicating greater fiber alignment, and higher energy, reflecting denser orientation information, compared with POAG eyes. These findings suggest that the structural properties of scleral fibers may differ between POAG and UG eyes at the stage when filtration surgery is required.