Electroretinography in streptozotocin diabetic rats following acute intraocular pressure elevation

BACKGROUND: We consider whether pre-existing streptozotocin induced hyperglycemia in rats affects the ability of the eye to cope with a single episode of acute intraocular pressure (IOP) elevation. METHODS: Electroretinogram (ERG) responses were measured (-6.08 to 1.92 log cd.s.m(-2)) in anaesthetized (60:5 mg/kg ketamine:xylazine) dark-adapted (>12 h) adult Sprague-Dawley rats 1 week after a single acute IOP elevation to 70 mmHg for 60 min. This was undertaken in rats treated 11 weeks earlier with streptozotocin (STZ, n = 12, 50 mg/kg at 6 weeks of age) or citrate buffer (n = 12). ERG responses were analyzed to derive an index of photoreceptor (a-wave), ON-bipolar (b-wave), amacrine (oscillatory potentials) and inner retinal (positive scotopic threshold response, pSTR) function. RESULTS: One week following acute IOP elevation there was a significant reduction of the ganglion cell pSTR (-35+ 11 , P = 0.0161) in STZ-injected animals. In contrast the pSTR in citrate-injected animals was not significant changed (+16 +/- 14 ). The negative component of the STR was unaffected by IOP elevation in either citrate or STZ-treated groups. Photoreceptoral (a-wave, citrate-control +4 + 3 , STZ +4 + 5 ) and ON-bipolar cell (b-wave, control +4 + 3 , STZ +4 + 5 ) mediated responses were not significantly affected by IOP elevation in either citrate- or STZ-injected rats. Finally, oscillatory potentials (citrate-control +8 + 23 , STZ +1 + 17 ) were not reduced 1 week after IOP challenge. CONCLUSIONS: The ganglion cell dominated pSTR was reduced following a single episode of IOP elevation in STZ diabetic, but not control rats. These data indicate that hyperglycemia renders the inner retina more susceptible to IOP elevation.