The effect of raised inspired carbon dioxide on developing rat retinal vasculature exposed to elevated oxygen

Hyperoxia is a risk factor for retinopathy of prematurity (ROP), a blinding disease in infants. However, ROP develops in human infants without raised arterial oxygen levels, such as in cyanotic congenital heart disease. In these infants raised pCO₂ may be a risk factor. We investigated the effect of inspired CO₂ on oxygen induced retinopathy in the rat. 56 newborn Sprague-Dawley rats were exposed to high cyclical O₂ for seven days. In a control group, 27 rats were exposed to negligible CO₂ by the use of soda lime. In the high CO₂ group, 29 rats were exposed to elevated CO₂ by omitting soda lime from their chambers. Rats in both groups had a recovery period of three days in room air following cyclical O₂ exposure. On the eleventh day all rats were sacrificed after intracardiac injections of fluorescein under deep anesthesia and the retinae were dissected and flat mounted for fluorescent microscopy. The ratio of vascularized-total retinal area was calculated using computer assisted image analysis. In the high CO₂ group 62% ± 7% SD of the retina was vascularized vs. 81 % ± 7% in low CO₂ group (p < 0.001). Elevated inspired CO₂ results in pronounced retardation of retinal vascular development in neonatal rats exposed to fluctuating raised oxygen. Curr. Eye Res. 13: 779-782, 1994.