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Visualization of the aqueous humor outflow pathway is undergoing a renaissance as new imaging technologies have enabled the first non-invasive visualization of the living functioning outflow tract in human eyes. In contrast, Hamanaka et al. employed standard light microscopy with immunohistochemical staining, and transmission electron microscopy to examine the distal outflow tract. In this study, the authors obtained tissue blocks from 133 patients undergoing trabeculectomy. Subjects were divided into three groups: (a) primary open-angle glaucoma (POAG) patients with a family history of POAG; (b) POAG patients without a family history of glaucoma; and (c) normal-tension glaucoma subjects. Tissue obtained during trabeculectomy was fixed, stained, and imaged, and approximately three images per sample were measured and averaged.
Visualization of the aqueous humor outflow pathway is undergoing a renaissance as new imaging technologies have enabled the first non-invasive visualization of the living functioning outflow tract in human eyes
They found that Schlemm's canal was significantly shorter in patients with a family history of POAG compared to those without. Staining of endothelial cells allowed accurate identification of Schlemm's canal, collector channels, and Sondermann's canals. Besides comparing Schlemm's canal morphology between groups, the authors are to be commended for the characterization of the other outflow structures of the proximal outflow pathway. The authors observed the segmental nature of Schlemm's canal, and a recurrent presence of Sondermann's canals within the trabecular meshwork. It is my hope that characterization of these structures concurrent with and IOP and disease data will contribute to the understanding of the complex structure-function relationship between age, disease, outflow pathway morphology, and the regulation of intraocular pressure.
Morphology/outflow and structure/function data notwithstanding, enjoy this paper for the outstanding images of outflow structures!