Functional and morphological studies of the primate outflow apparatus

The present investigation of the primate outflow apparatus comprises of two parts. Part I is concerned with the physiological and morphological effects of hyaluronidase on the outflow apparatus of the pig tailed macaque. Part II is a study of age-related changes in the human outflow apparatus. The aim of the first part of the investigation was to discover whether glycosaminoglycans in the trabecular meshwork, particularly the cribriform layer, contributed towards the resistance to aqueous outflow through this pathway. Nine pig tailed macaques (Macaca nemestrina) received an intracameral injection of 300 I.U. of testicular hyaluronidase (in 100 mul of Barany' s fluid) in one eye and the fellow eye served as a control, receiving Barany's fluid alone. One hour after the injections the flow rates at 18 mm Hg and 22 mm Hg from a perfusion system were determined in order to calculate outflow facility. The eyes were perfuse fixed in situ at 18 mm Hg, half an hour after the physiological determinations. Four eyes, two controls and two experimentals, were excluded from the study due to manipulative failures during the experiment. There was a great deal of variation in the results between animals. Despite this it was found that the flow rates in the hyaluronidase-treated eyes were significantly greater than the controls in three of five pairs at 18 mm Hg and in all five pairs at 22 mm Hg. Due to the variation between animals the group results did not prove to be statistically significant. There was no gross morphological difference between control and hyaluronidase-treated eyes, with the exception of slightly greater distension and fewer 'giant vacuoles' in the enzyme treated eyes. The outflow apparatus in both groups of eyes showed marked alterations in configuration compared with the normal unperfused tissue. These changes included rounding up of trabecular endothelial cells; disruption of the cribriform layer; "blow-outs" or focal ballooning of the lining endothelium of Schlemm's canal and herniation of cribriform tissue into collector channel openings. These changes were more severe than would have been predicted on the basis of pressure effects alone and may in fact have been due to physiological manipulation and over perfusion with mock aqueous. In Part II, a wide age range of human eyes, which had been immerse fixed after enucleation in the treatment of various ocular and orbital disorders of the posterior pole, were morphologically investigated. There was a great deal of variation in the morphological appearance of the outflow tissues not only between eyes of similar ages but also within one eye. Despite the variation, several age-related changes were qualitatively and quantitatively described. These included : the thickening of the trabeculae due to increased deposition of connective tissue elements; the trabeculae in older eyes often appeared denuded of their cell cover which seemed to cause focal degeneration and the release of connective tissue materials which appeared to accumulate in the outer meshwork; there was an increase with age in the electron dense plaques in the cribriform layer and a decrease in the ground substance; 'giant vacuoles' in the lining endothelium of Schlemm's canal were rare in older eyes (over 50 years); the incidence of localised canal closure due to apposition of the inner and outer walls was greater in older eyes. The present study of age-related changes in the human outflow apparatus will hopefully contribute to future morphological studies of the outflow apparatus from patients suffering from primary open angle glaucoma