The anatomy of the rabbit aqueous outflow pathway

. The morphology of the filtration angle and pathway of aqueous outflow was studied in 10 pigmented rabbits using light and electron microscopic techniques. The following conclusions were arrived at: 1. Numerous pectinate ligaments were found to cross the rabbit filtration angle. However, large spaces between these ligaments allows aqueous access to the peripheral portion of the angle and then to the trabeculum. The drainage of aqueous filtered through the meshwork is served by a plexus of 1 to 4 channels, which contain giant vacuoles along their internal and external walls. 2. A single layer of endothelial cells was found covering all meridians of the entire trabeculum from the termination of the cornea to the filtration angle recess. This layer, here termed the trabecular endothelial layer, is a continuation of the corneal endothelium, and it is accompanied by the posterior limiting lamina (Descemet's membrane) for its full length. 3. The aqueous passes through the trabecular endothelial layer by an intracellular route that possibly requires energy. 4. The presence of the trabecular endothelial layer in the rabbit may explain the variation that is known to exist between human and rabbit in responses to pharmaceutical agents. The physiology of the rabbit trabecular endothelial layer needs to be investigated to determine the suitability of this species as an animal model for the human glaucomatous conditions caused by the presence of such a layer.