Neuroretinal function during mild systemic hypoxia.

Few studies have investigated the effect of systemic hypoxia on the vascular and neural function of the human retina. Such studies can help us understand physiological responses to environmental hypoxia, as well as the pathophysiological mechanisms underlying certain ocular diseases. The objective of this study was to investigate the impact of mild systemic hypoxia on neuroretinal function through photopic flash electroretinogram (fERG) and oscillatory potential (OP) recordings.The photopic fERGs and OPs were recorded in 18 healthy adults under conditions of mild systemic hypoxia. The retinal responses were recorded before, during, and after a 5-min period of breathing 12% oxygen (O2) in 88% nitrogen. The heart rate (HR), respiratory rate (RR), end-tidal carbon dioxide pressure (Petco2), and O2 saturation (SaO2) were measured throughout testing. The systemic blood pressure (BP) and intraocular pressure (IOP) were measured to derive the ocular perfusion pressure (OPP).Systemic hypoxia reduced SaO2 and PetCO2, increased HR but did not alter the RR or OPP. The a-wave amplitude and latency were not altered throughout testing. The b-wave amplitude decreased with hypoxia, whereas its latency was not affected. The amplitude of OP1, OP2, and OP4 remained stable throughout testing, whereas the amplitude of OP3 tended to decrease with hypoxia and was increased at the end of testing. The latency of OP1, OP3, and OP4 did not vary. The latency of OP2 was reduced at the end of testing.Our results show that mild systemic hypoxia alters the fERG b-wave and OPs but not the a-wave. This suggests that the outer retina in humans is more resistant to a mild systemic hypoxic stress than the inner retinal layers.