Schwalbe line's cell in the normal and glaucomatous dog

Objective The canine iridocorneal angle contains an operculum, which is sim ilar to that in nonhuman primates and consists of a peripheral extension of the inner cornea that overlies the anterior-most portion of the corneoscle ral trabecular meshwork. This region contains cells, the Schwalbe line's (S L) cells, that have been found to have secretory and epithelial characteris tics. This region of the iridocorneal angle represents the nonfiltering por tion and becomes altered early during spontaneous glaucoma in the Beagle. T he present study describes the SL cell for the first time in the dog and ch anges associated with canine primary open angle glaucoma. Procedures The iridocorneal angles from IS Beagles with inherited glaucoma (3 months-8 years old) and 17 normal, age-matched Beagles were placed in 10 % buffered formalin for light microscopic evaluation, or 2.5% glutaraldehyd e for ultrastructural evaluation. Using at least three fields from each reg ion of die iridocorneal angle (opercular, corneoscleral, and uveal) at x 10 00 magnification, trabecular cell nuclei were counted. Results The operculum in the canine iridocorneal angle consisted of the per ipheral extension of the corneal endothelium and underlying anterior-most c orneoscleral meshwork, having no direct contact with the angular aqueous pl exus. The SL cells associated with operculum-retained epithelial morphology (polyhedral in shape with rER, Golgi apparatus, and secretory vesicles) in both normal, pre-and early glaucomatous dogs. In animals with moderate and advanced stages the SL cells often became less epithelial and secretory in appearance. The number of SL cells in normal dogs declined by approximatel y one-third by the end of their first year with gradual loss thereafter. In the glaucoma group the decline was more substantial and continuous through the first three years. Conclusions The SL cell is morphologically a distinct cell type within the canine iridocorneal angle that is specifically associated with the nonfilte ring portion of the corneoscleral trabecular meshwork. Changes in the SL ce lls of the glaucomatous dog occurred with regard to age and progression of the disease.