The morphology of the outflow apparatus of the eye with particular reference to its structural appearance at various levels of intraocular pressure

Grierson, Ian (1976) The morphology of the outflow apparatus of the eye with particular reference to its structural appearance at various levels of intraocular pressure. PhD thesis, University of Glasgow.

Abstract

The morphology of the outflow apparatus, the tissues through which the bulk of the circulating aqueous humour within the eye must pass to reach the venous system, has been studied by light microscopy, transmission electron microscopy and scanning electron microscopy. The two part investigation describes the appearance of a) the normal outflow apparatus in four species (human, baboon, rhesus monkey and rabbit) and b) the rhesus monkey outflow apparatus at various maintained levels of intraocular pressure (O, 8, 15, 22, 30 and 50 mm Hg). Cellular adhesion in the delicate meshwork tissues was enhanced by the presence of small punctate intercellular junctions one of which, a macular gap junction, has not previously been described at this site. The presence and significance of mucopolysaccharides in the drainage system has been the subject of much debate. In the present study, complex polysaccharides were consistently demonstrated in all four species. It was speculated that a prominent hydrophilic network of mucopolysaccharides, particularly in the endothelial meshwork, may have a significant influence on the rate of fluid passage through the outflow apparatus. On anatomical grounds, the intercellular clefts of the endothelium lining the trabecular aspect of Schlemm's canal were considered to be leaky. Intercellular passage of fluid was not thought to make a significant contribution to bulk outflow. A system of large vacuolar and non-vacuolar transcellular channels were thought to be a more effective route for ciqueous drainage into Schlemm's canal. To investigate the morphology of the rhesus monkey outflow; apparatus at various pressure levels, the appropriate pressures were maintained for one hour and, thereafter, the tissue fixed at approximately the same pressure level. At 0 mm Hg the outer meshwork was compressed and the canal endothelium contained neither vacuoles nor transcellular channels. The meshwork and the overlying canal endothelial monolayer was an effective barrier to the passage of red cells into the anterior chamber. With progressive pressure elevation, the meshwork became more and more distended to the highest pressure in the series (50 mm Hg). That tissue disruption was found only at 50 mm Hg emphasised the effectiveness of the junctional adhesive mechanisms in binding the pliable meshwork cells together. Associated with the progressive meshwork distension was an increase in the incidence of giant vacuoles, vacuolar transcellular channels and non-vacuolar transcellular channels up to 30 mm Hg. Within the range 8 to 30 mm Hg the relationship between vacuole numbers and intraocular pressure was linear whereas, as a result of dimensional changes to the vacuoles, the relationship between vacuolar carrying capacity and intraocular pressure was non-linear. The findings indicated that bulk outflow was accomplished by a system of temporary pressure dependent intracellular flow pathways. At 50 mm Hg aqueous outflow was non-physiological since canal occlusion vacuole drainage and endothelial disruption was extensive. The significance of meshwork pliability and variable porosity in the canal endothelium to ocular homeostasis, tissue function and disease processes was discussed.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: W R Lee
• Keywords: Ophthalmology, Morphology
• Date of Award: 1976
• Depositing User: Enlighten Team
• Unique ID: glathesis:1976-73957
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jun 2019 08:56
• Last Modified: 14 Jun 2019 08:56
• URI: https://theses.gla.ac.uk/id/eprint/73957