Electroretinographic assessment of retinal function during acute exposure to normobaric hypoxia

The current study aimed to investigate retinal function during exposure to normobaric hypoxia. Standard Ganzfeld ERG equipment (Diagnosys LLC, Cambridge, UK) using an extended ISCEV protocol was applied to explore intensity-response relationship in dark- and light- adapted conditions in 13 healthy volunteers (mean age 25 +/- 3 years). Baseline examinations were performed under atmospheric air conditions at 341 meters above sea level (FIO2 of 21 %), and were compared to hypoxia (FIO2 of 13.2 %) by breathing a nitrogen-enriched gas mixture for 45 min. All subjects were monitored using infrared oximetry and blood gas analysis. The levels of PaCO2 changed from 38.4 +/- 2.7 mmHg to 36.4 +/- 3.0 mmHg, PaO2 from 95.5 +/- 1.9 mmHg to 83.7 +/- 4.6 mmHg, and SpO(2) from 100 +/- 0 % to 87 +/- 4 %, from baseline to hypoxia respectively. A significant decrease (p < 0.05) was found for saturation amplitude of the dark-adapted b-wave intensity-response function (Vmax), dark-adapted a- and b-wave amplitudes of combined rod and cone responses (3 and 10 cd.s/m(2)), light-adapted b-wave amplitudes of single flash (3 and 10 cd.s/m(2)), and flicker responses (5-45 Hz) during hypoxia compared to baseline, without changes in implicit times. The a-wave slope of combined rod and cone responses (3 and 10 cd.s/m(2)) and the oscillatory potentials were significantly lower during hypoxia (p < 0.05). A isolated light-adapted ON response (250 ms flash) showed a reduction of amplitudes at hypoxia (p < 0.05), but no changes were observed for the OFF response. The results show significant impairment of retinal function during simulated normobaric short-term hypoxia affecting specific retinal cells of rod and cone pathways.