The effect of in vivo retinal cooling on the electroretinogram of the rabbit

PURPOSE Studies reporting the effect of retinal cooling on the electroretinogram of mammals have, in most cases, made use of an in vitro approach where the temperature of the retina was lowered by reducing the temperature of the bathing media. The purpose of our study was to investigate, in rabbits, the effect of in vivo retinal cooling using an experimental approach never before reported in order to determine if some of the temperature-related ERG effects previously shown could have been, in part, amplified by alterations in the physiological status of the retina due to preparation for in vitro study. METHODS In order to reduce the temperature of the retina, a 20 gauge plastic tubing was coiled around the eye from the limbus to the optic nerve head and glued to the sclera. Cold (15 degrees C) tap water entered the tubing at the limbal extremity and exited (18 degrees C) at the optic nerve extremity. Intraretinal temperature was measured to be within 1 degrees C of that of the circulating water. RESULTS Our results indicate that with progressive retinal cooling the a- and b-waves are gradually reduced to 66.9 +/- 17.3 and 90.9 +/- 10.4% of control respectively. The most dramatic temperature induced ERG modifications were observed in the oscillatory potential recordings where the mean summed OP amplitude (OP2 + OP3 + OP4) was reduced to less than 23.9 +/- 13.5% of control with OP2 being the least affected. The peak times of all the ERG components were significantly delayed with cooling. CONCLUSIONS Of all the ERG components examined, the OPs were those most severely affected by our manipulation. We believe that our results constitute further evidence in support of the concept that the OPs are more sensitive to retinal disturbance than the b-wave.