mfERG Evidence Suggesting That the Central Retina Is Affected First Following Postnatal Hyperoxia

Abstract

Abstract: : Purpose: We have previously shown that postnatal hyperoxia induces a severe and irreversible pan–retinal retinopathy as evaluated with the flash ERG and histology. The purpose of this study was to determine, using the multifocal ERG (mfERG), whether we could identify regional differences in retinal susceptibility to postnatal hyperoxia. Methods: Newborn Sprague Dawley rats were exposed to 22.5 hours of 80% O₂ interrupted by 3 periods of 0.5 hours at 21% O₂. Rats were grouped at birth into three exposure regimens; postnatal days 0–6 (n=6), 6–14 (n=6), 0–14 (n=6) and one control group raised in 21% O₂ (n=6). mfERGs (VERIS 4.8; camera display unit) were recorded (bandwidth: 10–100Hz) at postnatal day 60 using 37 hexagons (white: 200cd.m^–2s; black: <2 cd.m^–2s; background: 50 cd.m²) using an m–sequence of 4–minute duration (interframe interval: 13.3ms). Data analysis was limited to the first order kernel and results were compared to those obtained with the photopic flash ERG (intensity: 0.9 log cd.m².sec; background: 30cd.m^–2). Results: The summed response of the 37 hexagon matrix revealed a significant and equal attenuation in amplitude for all exposure regimens (P0–6: 20.6±8.9%, P6–14: 19.8±7.6%, P0–14: 16±3.4%, of control) compared to photopic flash ERGs which revealed significant amplitude attenuations only following exposures that included at least the second week of life (P0–6: 87.2%, P6–14: 38.7%, P0–14: 25.4%, of control). Furthermore, mfERGs evoked from inferiorly located hexagons were significantly more reduced (P<0.05) compared to the other retinal locations in animals exposed to hyperoxia. Conclusions: Our results show that the mfERG is affected maximally following exposure from P0–6, while the photopic flash ERG becomes progressively worse resulting in an amplitude attenuation comparable to that obtained with the mfERG only following a 14–day exposure. This would suggest that cones located in the central retina are more susceptible to hyperoxic insult than those in the periphery. These results would further support our previous demonstration of an abnormal central retinal vasculature in addition to an abnormal flash VEP following O₂ exposure during the same period.

Keywords: retinopathy of prematurity • electroretinography: non-clinical • oxidation/oxidative or free radical damage