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RGC Sensitivity to Mild Systemic Hypoxia

From the University of Montreal, School of Optometry, Montreal, Quebec, Canada.

PURPOSE. Systemic hyperoxia, hypercapnia, and hypoxia are known to alter retinal perfusion. The effects such experimentally induced systemic blood gas perturbations have on inner neuroretinal function in humans were examined.

METHODS. Twenty healthy adults participated in each of three test sessions. The effects of breathing pure oxygen (O₂), carbogen, or a hypoxic gas on the pattern electroretinogram (pERG) were investigated. The stimulus consisted of high-contrast, black-and-white, 48-min arc checks reversing at 1 Hz. pERGs were recorded with a Dawson-Trick-Litzkow electrode at the end of 5 minutes of breathing room air, 5 minutes of breathing the test gas, immediately after the flow of gas was stopped, and 10 minutes after the flow of gas was stopped.

RESULTS. Amplitudes and implicit times of the major positive (P50) and negative (N95) components of the pERG were not altered during the pure O₂ and carbogen breathing sessions. Although the amplitude and implicit time of P50 were not modified significantly with systemic hypoxia, they were depressed and delayed, respectively, for N95.

CONCLUSIONS. Inner neuroretinal function remained unchanged during increased blood O₂ and carbon dioxide levels known to alter retinal blood flow, but it was altered during decreased blood O₂ levels. Overall, these results indicate that the generators of P50 are resistant to systemic hyperoxia, hypercapnia/hyperoxia, and hypoxia. They further indicate that the generators of N95, namely the retinal ganglion cells, are particularly sensitive to transient, mild systemic hypoxia.

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