Effects of increased intraocular pressure on rat retinal ganglion cells^†

The effects of elevated intraocular pressure (IOP) on the morphology of rat retinal ganglion cells (RGCs) was analyzed in this study. After cauterizing two limbal derived episcleral veins, IOP in experimental eyes was elevated 1.5–1.8 times that of control. RGCs of experimental and control eyes were analyzed after: bilateral tectal injections of Fluoro-Gold, and application of fluorescent dye crystals, 4-Di-10-ASP to the proximal stump of the cut optic nerve, at different time intervals after IOP elevation. The RGCs in control and experimental eyes were evaluated at 4, 6, 8, and 10 weeks by counting, as well as by determining the soma diameter. The dendritic field of three types (I, II, III) of RGCs between control and experimental eyes were also studied at 4,6,10 weeks after IOP elevation. At every time point, the number of cells in experimental eyes were significantly less than those of the control eyes. The average retinal ganglion cell death was 3–4% per week in the eyes with elevated IOP. The soma and dendritic field diameter of the RGCs in the experimental eyes were significantly larger in all cell types. However, types I and III cells expanded their dendritic fields more rapidly than type II cells. Furthermore, dendritic fields of surviving RGCs in experimental eyes occupied about the same extent of the retina as the controls. The increase in soma diameter and expansion of dendritic fields in the remaining RGCs in eyes with elevated IOP suggests the existence of plasticity in adult retina.