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MA Johnstone, R Stegmann, BA Smit; Unique Cylindrical Structures Spanning From TM Across SC Newly Identified During Unroofing of the Canal: Correlation With Histologic Findings . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1935.
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Purpose: To compare unique structures spanning Schlemm's canal (SC) identified by canal unroofing with laboratory evidence of endothelial-lined tubular channels spanning SC. Such channels have been previously implicated as a mechanism for aqueous passage to SC1. Methods: Clinical- In 10 human eyes undergoing viscocanalostomy, structures spanning SC were identified during canal unroofing. Video documentation was used to assess anatomic features, effects of SC unroofing and of micromanipulation. Laboratory- In 16 necropsy eyes (8 human, 8 primate) viscoelastic was introduced into SC. Preparation involved 500 µ sections, epon embedded 1 µ sections and SEM segments. Five additional living rhesus monkey and 2 human autopsy eyes underwent experimental studies and were then examined by light, transmission (TEM) and scanning electron microscopy (SEM). Nucleated avian RBC's were introduced into the AC as tracers in 2 of the living primate and 1 human eye. Prior to in vivo fixation IOP was lowered in the 5 primate eyes to permit blood to reflux into SC as an additional tracer. Results: Clinical-Diaphanous cylindrical stuctures, which by retro illumination could be seen to contain a lumen, spanned between the TM and corneoscleral wall of SC. The structures were highly compliant and by micromanipulation could be stretched to over twice their resting length. As many as 10 such structures were identified in an unroofed 5 mm region of SC in children. Laboratory-In human and primate eyes, light, transmission and SEM demonstrated endothelial tubular channel origins from the trabecular meshwork, their attachment to the corneoscleral wall of the canal and openings at their distal end. SC dilation by viscoelastic revealed diaphanous cylindrical structures spanning the canal easily seen with the dissecting microscope. By examining the entire circumference of SC in 500 µ segments, frequency of the structures was determined to be 2/mm in primate eyes. Avian RBC's introduced into the AC as tracers entered the proximal lumen of the structures. Primate RBC's introduced into SC as tracers entered the distal lumen of the structures. Conclusion: Clinical and laboratory studies demonstrate unique anatomic entities consisting of cylindrical tubular structures spanning SC. Anatomic appearance & tracer studies suggest the structures can transport aqueous to SC and thus merit further study. 1. Johnstone, MA Pressure-dependent changes in configuration of the endothelial tubules of Schlemm's canal in the cynomolgus monkey AJO. 78:630, 1974
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