RETINAL GANGLION-CELL DEATH AFTER DIFFERENT TRANSIENT PERIODS OF PRESSURE-INDUCED ISCHEMIA AND SURVIVAL INTERVALS - A QUANTITATIVE IN-VIVO STUDY

Purpose. To quantitate in vivo retinal ganglion cell (RGC) survival af ter transient periods of pressure-induced ischemia of the rat retina a nd after different survival intervals. Methods. In adult rats, RGCs we re labeled with fluorogold applied to their main targets in the brain, Seven days later, in several groups of rats, the left retinas were su bjected to transient periods of ischemia of 30, 45, 60, 75, 90, 105, o r 120 minutes, respectively, by increasing the intraocular pressure (I OP) of the left eye above systolic values, Five, 7, 14, and 30 days la ter, the rats were killed, and their retinas were prepared as whole mo unts for examination under fluorescence microscopy to estimate RGC sur vival. Results. The authors found that periods of ischemia of 30 and 4 5 minutes do not induce RGC death; longer periods of transient ischemi a induce the death of a proportion of RGCs, and the proportion increas es with the duration of the ischemia; RGC death, which can be observed as early as 5 days after ischemia, continues during die 30-day study period; and periods of ischemia that last 90 minutes or more cause the death of approximately 95% of tile RGC population 30 days later, Conc lusions. Increases of the IOP above systolic levels for periods of 60 minutes or more result in RGC loss in the rat retina. Both the duratio n of the initial transient period of ischemia and the duration of the survival period influence the proportion of RGC death.