HISTOPATHOLOGICAL EVALUATION OF RETINAL DAMAGE DURING INTRAOCULAR HYPERTENSION IN RABBIT - INVOLVEMENT OF GANGLION-CELLS AND NERVE-FIBER LAYER

Background: Current clinical tests do not detect glaucomatous signs un til the onset of substantial retinal damage. Therefore animal models a re required to investigate the very early histopathological alteration s in glaucoma disease. We used an experimental model of intraocular hy pertension to compare early changes in retinal ganglion cell (RGC) den sity with the thickness of the nerve fiber layer (NFL). Methods: Methy lcellulose 2% was injected into the anterior chamber of 18 eyes of 18 New Zealand albino rabbits. Intraocular pressure was measured 6 h afte r the injection and thenceforth once a day using a Shiotz tonometer. H istopathological analysis was performed on days 4, 10, and 15 followin g the induction of hypertension (six eyes for each group). Sections fr om the upper temporal retina were stained with hematoxylin-eosin and i mmunohistochemically using a polyclonal antibody PGP 9.5 to identify R GC. An image analysis system was used to evaluate the RGC and the thic kness of the NFL. Results: We observed a significant increase in intra ocular pressure until the end of the experiment. Histological analysis showed, after 10 days of ocular hypertension, a significant decrease in RGC density (P<0.05) and a significant increase (P<0.05) in glial c ell density. We found a significant correlation between RGC loss and c ell area at 4 days (P<0.01; Cc=0.86) and at 10 days (P<0.002; Cc=0.91) of intraocular hypertension. We did not observe a significant decreas e in the NFL thickness until 10 days of intraocular hypertension. Conc lusions: Our study confirms the size-dependent RGC loss during intraoc ular hypertension and shows no early decrease in NFL thickness.