Episclera: a scleral tissue rich in reticular fibers.

PURPOSE: To determine the episcleral area based on the distribution of reticular fibers. METHODS: Central sagittal sections from East Asian cadavers fixed in 10% formalin were examined. The episclera and scleral stroma were evaluated at the pars plana and the 3:00-3:30 and 5:00-5:30 clock-hour positions. Sections were stained with silver impregnation and type III collagen immunostaining. RESULTS: Eleven globes from 10 cadavers aged 36-94 years (mean, 70.8 years) were analyzed. The episclera and scleral stroma were clearly visualized with silver impregnation. The mean diameters of silver-positive fibers in the episclera and scleral stroma were 0.73 μm (median [interquartile range: IQR], 0.77 [0.49-0.94] μm) and 2.58 μm (median [IQR], 2.83 [1.79-2.96] μm) at the pars plana; 0.59 μm (median [IQR], 0.60 [0.29-0.77] μm) and 2.52 μm (median [IQR], 2.63 [1.72-3.26] μm) at 3:00-3:30; and 0.70 μm (median [IQR], 0.66 [0.56-0.93] μm) and 2.04 μm (median [IQR], 1.79 [1.38-2.65] μm) at 5:00-5:30. Fibers were significantly thinner in the episclera than in the scleral stroma (p = 0.003). The episclera showed strong type III collagen immunostaining, whereas the adjacent scleral stroma showed little staining for type III collagen. The episclera accounted for 15%, 4%, and 12% of the total scleral thickness at the three regions, respectively. CONCLUSION: The episclera could be defined as the outer thin area of the sclera, rich in reticular fibers. These anatomical features enhance understanding of episcleral structure and highlight its clinical relevance. This study provides a foundation for future imaging-based investigations.