Post-ischemia ERG recovery is influenced by temperature

In experimental work on retinal ischemia and its medical management, we have been disturbed by the large variations in the electroetinogram (ERG) recovery of rabbit eyes subjected to similar degrees of ischemia. We investigated whether body temperature might be one of the critical factors. We studied pigmented Dutch rabbits that had been subjected to 60 min of ocular ischemia followed by 4 h of reperfusion at different body temperatures. Ischemia was produced by cannulating the anterior chamber and raising the intraocular pressure. Scotopic ERGs and rectal temperatures were recorded at regular intervals. Rabbits with a subnormal mean temperature of 35.5-37.7 degrees C throughout the experiment showed mean a- and b-wave recoveries of 131.52% and 107.68% of preischemic values after 4 h reperfusion. At temperatures between 37.8-38.9 degrees C, the a- and b-waves only recovered to 88.43% and 32.0% respectively. Even small degrees of cooling greatly enhanced post-ischemic ERG recovery. This may explain some of the variations in ERG recovery that have been reported in the literature. We suggest that body temperature should be tightly controlled between 37.8 and 38.9 degrees C during ischemia experiments to stabilize results and minimize errors in judging therapeutic effects. Retinal cooling may be a means to protect the retina against ischemic damage in clinical situations.