Abstract
PURPOSE: To microscopically examine the lymphatic characteristics of the outflow tract of aqueous humor in humans. METHODS: Central sagittal sections (12 o'clock direction) of 15 ocular angle areas with sclera and conjunctiva (8 right, 5 left) from 14 Japanese cadavers, aged 36-94 years (average age: 73.0 years) were histologically examined. The specimens were fixed in 10% formalin. Staining with D2-40 was utilized to identify lymphatic channels. RESULTS: The trabecular meshwork and Schlemm's canal exhibited D2-40 staining in all specimens. The collector channels demonstrated three staining patterns. Type 1 (2 specimens) showed strong staining that was distributed from the trabecular meshwork to the subconjunctival lymphatics throughout the sclera. Type 2 (6 specimens) had strong staining around the trabecular meshwork, Schlemm's canal, and proximal collector channels, but had thinner staining across the sclera. In the third type (7 specimens), the staining was limited to the trabecular meshwork, the Schlemm's canal, and/or the proximal collector channels. Specimens from individuals younger than 70 years predominantly exhibited type 1 and type 2 patterns. In contrast, older specimens from individuals older than 70 years of age mostly displayed type 2 and type 3 patterns, indicating reduced lymphatic staining of the sclera with age. CONCLUSION: The outflow pathway of the aqueous humor demonstrated lymphatic characteristics, with D2-40 staining of the trabecular meshwork, Schlemm's canal, and proximal collector channels in all specimens. However, the extent of collector channel staining varied, with older specimens showing less staining in the sclera. This suggests age-related changes in lymphatic distribution.