A morphologic and morphometric analysis of the aqueous outflow system of the developing cat eye.

The cellular and tissue changes accompanying the development and growth of the aqueous outflow system of the cat were investigated by quantitative light microscopy and by scanning and transmission electron microscopy. As in primates, the trabecular beams and sheets of the cat aqueous outflow system developed by reorganization of cells and extracellular matrix within the tissue filling the anterior chamber angle recess. Enlargement and coalescence of intercellular spaces gave rise to intertrabecular channels. From 3 to 9 days after birth, communications were established between the anterior chamber and intertrabecular spaces by perforation and resorption of tissue which initially covered the angle apex and appeared to be a peripheral extension of Descement's membrane and the corneal endothelium. Macrophage-like cells could be involved in this process. A rapid increase in the volume of the intertrabecular spaces and in the number of trabecular cells coincided with the opening of the trabecular meshwork to the anterior chamber. The trabecular meshwork grew 150-fold in volume from birth to adulthood, mainly as a result of a similar-fold expansion of its connective tissue components. The volume of the intertrabecular spaces increased 24-fold and trabecular cell number increased 14-fold during this same period. The disproportionate increase in volume of the various components of the trabecular meshwork was responsible for the decreased cell density and rarefaction displayed by this tissue as development progressed. Development of the aqueous outflow system of the cat is thus a complex, but highly co-ordinated, process, that depends on continued proliferation of cells and extracellular matrix, a progressive ordering of these components, and selective atrophy and removal of specific tissue components.