MORPHOLOGICAL CHARACTERIZATION OF THE UVEOSCLERAL PATHWAY IN NORMAL AND GLAUCOMATOUS DOGS

Abstract

Abstract: : Purpose:To date, our knowledge of the canine uveoscleral (US) pathway with regard to its anatomy is insufficient. It is important to understand the construction of this pathway for normal aqueous humor outflow and possible changes associated with spontaneous hypertensive glaucoma, especially with regard to its potential role for prostaglandin therapy. To that end, we have examined the US pathway in the normal and glaucomatous canine eyes morphologically and immunohistochemically. Methods:Specimens from the anterior uveas of 10 Beagles with inherited glaucoma (3 mos to 6 yrs old) and age–matched normal Beagles, and 4 Cocker Spaniels with spontaneous glaucoma were serially sectioned sagittally and then tangentially. Every tenth section was treated with a particular stain that included: H&E, Masson’s trichrome, smooth muscle actin immunolabel, and elastin stain. Results:Within normal specimens outer uveal trabeculae of the iridocorneal angle (ICA) formed tendinous endings of the outer ciliary body musculature (CBM) and spaces between these endings formed the major avenues for the beginning of the US pathway. In addition, other muscle bundles anteriorly attached the CBM to the sclera concomitant with the presence of an anterior elastic sheath. Posteriorly within the US pathway, sparsely populated trabeculae and infrequent smooth muscle ‘pegs’attached the outer CBM to the adjacent sclera. Age–related changes were minimal. Among the glaucomatous specimens, the sparsely trabeculated space of the US pathway was recognizable in most instances. The outer anterior elastic sheath was especially developed, as well as the presence of melanophores within the US pathway and adjacent neighboring vessels. Conclusions:The normal morphology of the US pathway is well defined by the time that the canine eye is fully developed, changing little with age. While marked changes occurred within the ICA of specimens with advanced glaucoma, alteration of the US pathway was less affected, indicating that it plays an increasingly important role in aqueous humor dynamics within the canine glaucomatous eye regardless of breed and that this role could be expanded therapeutically.

Keywords: outflow: ciliary muscle • anatomy • aging