Electroretinogram Findings in Animal Model of Concurrent Diabetes and Hypothyroidism

Abstract

Purpose: Investigate the retinal functional impairment due to concurrent diabetes and hypothyroidism using electroretinogram (ERG).

Methods: 16 Wistar rats (Rattus norvegicus) with two-months-old, were divided in four groups: control (glucose: 80.7±15.2; weight: 165.1±9.2); group with hypothyroidism induced by bilateral thyroidectomy (glucose: 84.4±12.1mg/dl; weight: 157.2±9.7g); group with diabetes induced by injection of 2% alloxan (200 mg/kg) intraperitoneally (glucose: 389.6±87.3mg/dl; weight: 189.7±12.8g); group with both, diabetes and hypothyroidism (glucose: 412.1±70.04mg/dl; weight: 187.53±14g). After 30 days of treatment electroretinograms were obtained using flash stimuli to evaluate physiological changes in scotopic and photopic light adaptation. Rod driven ERGs were obtained with 10 cd/m².s flash after two log units attenuation. Mixed rod-cone driven ERGs were elicited with 10 cd/m².s stimulation after 12 hours scotopic adaptation. Cone driven ERGs were obtained with 10 cd/m².s stimulation after 10 minutes photopic adaptation.

Results: There was a decrease in the average amplitude of the a- and b-wave in animals with diabetes and both metabolic diseases in all light adaptations. When comparing the group with diabetes and the group with hypothyroidism, it was clear that diabetes provoked greater decrease in ERG amplitude (one-way ANOVA, p= 0.05). Moreover, the animals with both diseases showed a synergistic action of diabetes and hypothyroidism as verified by ERG amplitude decrease. In combined response (rods and cones) the highest statistical differences among groups were found. The mean a- and b-wave amplitude values were a-79.71 µV (±15.18) and b-99.95 µV (±30.60) for the group with both diseases; a-100.4 µV (± 13.31) and b-165.7µV (± 20.85) for the group with diabetes; a-160 µV (± 19.72) and b-280.3 µV (± 54.47) for the group with hypothyroidism; a-179.3 µV (± 22.79) and b-332.3 µV (± 57.53) for control group.

Conclusions: The results support the hypotheses that both, photoreceptors and inner layers of the retina were affected by both diseases, but remarkably by diabetes. All ERG responses were significantly impaired, mainly those recorded after scotopic adaptation

Keywords: 510 electroretinography: non-clinical • 688 retina • 498 diabetes