Research Progress on the Morphology of the Schlemm’s Canal

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Research Progress on the Morphology of the Schlemm’s Canal

Journal Title: Biomedical Journal of Scientific & Technical Research (BJSTR) - Year 2019, Vol 19, Issue 1

Abstract

Glaucoma is one of the leading causes of blindness worldwide. High intraocular pressure (IOP) contributes to the development and progression of the condition. Although the specific mechanism underlying IOP increase in glaucoma remains elusive, it is clear that the Schlemm’s Canal (SC) is a crucial structure in regulating IOP and a potential therapeutic target Hou et al. [1]. With the advancement of inspection techniques, we can obtain high-quality images of the SC, which facilitates quantitative measurements and improves the understanding of the SC structure. In this review, we summarized the current data about the morphological changes in the SC under physiological, pathological, and post-treatment states.In 1830, the Schlemm’s Canal (SC) was first described and named by Schlemm, a German anatomist Hamanaka and Ujike [2], and was considered an important pathway in draining aqueous humor into the circulation system and an important structure of the blood–aqueous barrier. SC is a ring-shaped vessel located at the inner part of the corneoscleral junction, where it links the trabecular meshwork (TM) and collector duct. The SC area estimated via histological staining was 1709 μm2. However, the in vivo, noninvasive optical coherence tomography (OCT) showed that the SC areas vary from 4064 to 7164 μm2 Dautriche et al. [3]. Due to the difference in microenvironment, the endothelium of the SC is not equal. The endothelial cells near the TM comprise the inner wall, and the remaining is referred to as the outer wall. The inner wall has been extensively explored as the increase in IOP in primary open-angle glaucoma (POAG) was found to be mainly correlated to the increased resistance of the inner wall and juxtacanalicular tissue Overby et al. [4]. Under the electron microscope, the inner wall is characterized by a smooth nucleus projected into the SC, and numerous giant vacuoles and pores could be observed in the inner wall cells. Giant vacuoles were considered to be linked cell processes, or invaginated juxtacanalicular cytoplasm, whereas the pores were the inner wall structures, which regulated aqueous flow into the SC Dautriche et al. [3]; Fink et al. [5]. Moreover, unlike normal vascular endothelial cells, the basement membrane beneath the inner wall is incomplete and the direction of pressure on the endothelial cells is different. The stress direction of normal vascular endothelial cells is from the top to the bottom, whereas that of the SC endothelial cells is opposite. Thus, the SC is more at a risk of deformation and collapse Ramos et al. [6]; Raviola and Raviola [7]. In addition, to maintain the function of the blood–aqueous humor barriers, the SC maintains a relatively closer connection between the endothelial cells, indicating that it has greater pressure difference when facing the same volume of reflux liquid Bhatt et al. [8]; Ramos et al. [6].

Authors and Affiliations

Qingfeng Liang, Leying Wang, Guanyu Su, Ningli Wang

Keywords

EP ID EP622544
DOI 10.26717/BJSTR.2019.19.003258
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