Role of cameral mucous gel in primary narrow angle and closed angle glaucoma: a pathogenic clue

The cameral mucous gel (CMG) has been described as a layer of glycoprotein-enriched hyaluronic acid lining the anterior surface of the iris, covering the trabecular meshwork, and spreading over the posterior surface of the cornea. The CMG is thought to exert a colloid-osmotic effect on the hydrostatic forces involved in the circulation of the aqueous humour which may help our understanding of the pathophysiology of open angle and angle closure glaucomas. The CMG was precipitated in two normal human eyes, one with an artificially shortened anterior chamber and the other with an open chamber. In the eye with a narrow angle, the CMG was seen to fill the iridocorneal gap completely, blocking access to the trabecular meshwork from the central anterior chamber. The CMG may be implicated in the pathogeny of narrow angle and closed angle glaucoma. The two types of glaucoma may share a common mechanism depending on the thickness of the layer of CMG that precedes the exit pathways. Pretrabecular CMG thickness is a decisive determinant of the colloid-osmotic resistance of the gel to aqueous outflow, and this thickness is governed by, among other factors, the position of the iris relative to the posterior surface of the cornea. The formation of a thick layer of CMG in the narrow chamber angle prevents the normal anterior chamber pressure from exerting a backward displacement effect on the peripheral iris. Unopposed posterior chamber pressure may therefore force the peripheral iris forward, making angle closure likely.