The effect of acute hypoxia and hyperoxia on the slow multifocal electroretinogram in healthy subjects

Purpose. To characterize the topographic response of the healthy human retina to acute oxygenation changes in vivo, using multifocal electroretinography (mfERG). Methods. Ten eyes in 10 subjects were examined while they breathed 21% oxygen (normoxia), 10% oxygen (hypoxia, with 90% nitrogen), or 100% oxygen (hyperoxia). Capillary oxygenation was monitored by percutaneous infrared oximetry. Results. Compared with normoxia (mean Pao(2), 124 mm Hg), hypoxia (mean Pao(2), 36 mm Hg) was associated with an overall mfERG amplitude reduction, including a reduction in the multifocal oscillatory potentials (mfOPs). The hypoxic amplitude reduction of the first- order P1 response decreased monotonically (P < 0.0001) from 38.5% at 0 degrees to 2 degrees eccentricity to 17.8% at the highest eccentricity (25 degrees). Likewise, the amplitude reduction of first-order N2 decreased from 33.0% centrally to 18.3% at the highest eccentricity (P = 0.0019). In contrast, hypoxia only reduced the average first-order N1 amplitude by 9.5% (P = 0.016). Hypoxia also reduced mfOP amplitudes, by 16.6% to 34.8%, but no effect of eccentricity was detectable. Hyperoxia had no significant effect on amplitude. Neither hypoxia nor hyperoxia had any effect on the latency of the P1 implicit times. Conclusions. The present study demonstrated regional differences in response to hypoxia. The origin of this difference is not known but may be explained by a combination of differences in cone structure, circulation of different regions, or differences in the microenvironment around different cones. The function of the central retina is expected to be more susceptible to the hypoxia that may occur in disease. The relative effect of hypoxia on the photopic N1 and P1 is similar to that on the scotopic a- and b- wave in other mammals, and the present work extends the current knowledge by showing regional effects that were previously undetected.