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Aims-Hypothermic irrigating solutions were used during vitrectomy in pressure induced ischaemic eyes so that their eVects on retinal function and histological changes could be investigated. Methods-After anaesthetised albino rabbits underwent closed vitrectomy, their vitreous cavities were continuously irrigated for 30 minutes at a perfusion pressure of 140 mm Hg. The rabbits were divided into three groups according to their intraocular perfusion temperatures-8°C, 22°C, and 38°C. Electroretinograms were taken before and after irrigation. Glutamate levels in the vitreous were examined after irrigation. Eyes were enucleated on the seventh postoperative day and examined histologically. Results-On the seventh postoperative day, the recovery rate of a-wave amplitudes was significantly lower in the 38°C group than in the 8°C group, and that of b-wave amplitudes was significantly lower in the 38°C group than in either the 8°C or 22°C group. Retinal damage in the 38°C group revealed more severe histological impairment than in either the 8°C or 22°C group. Oedema of the inner retinal layer was significant in both the 22°C and 38°C groups. Glutamates reached peak values 30 minutes after the end of ischaemia in the 38°C group. However, no significant glutamate increases were detected 15 to 60 minutes after ischaemia in either the 8°C or 22°C group. Conclusion-Local hypothermia during vitrectomy in acute ischaemic eyes appears to decrease retinal damage. (Br J Ophthalmol 1997;81:789-794) Hypothermia is known to increase tissue tolerance to ischaemic insults, 1 and has been applied in neurosurgery 2 and cardiac surgery. Hypothermic neuroprotective properties are well documented in brain damage, 4 the eVects being partly due to reducing the ischaemia induced release of excitatory amino acids. 5The application of hypothermia in vitreous surgery has recently been investigated. [6][7][8][9][10][11][12] Hirose et al 12 reported that chilled solutions were useful during vitreous surgery for advanced stages of retinopathy of prematurity in order to prevent or minimise fibrin formation. We 11 reported in a previous paper that local hypothermia during vitrectomy reduced retinal damage in pressure induced mild ischaemia. Several factors, including excitatory amino acids and free radicals, are known to be related to retinal damage resulting from ischaemia and subsequent reperfusion. [13][14][15] However, the mechanisms for hypothermic eVects on an ischaemic retina have not yet been substantiated.In this study, we performed intravitreous irrigation under complete vaso-occlusive pressure using solutions at various temperatures, while examining the electrophysiological and histological changes of the retina. We also measured changes in glutamate levels in the vitreous after ischaemia. Materials and methods VITRECTOMY AND SUBSEQUENT VITREOUS PERFUSIONTwenty five albino rabbits were anaesthetised with intravenous injections of pentobarbitone 20 mg/kg. Their pupils were dilated with a 1:1 mixture of 0.25% tropicamide and 5% phenyl...