PURPOSE - Present technologies are not able to determine which retinas are at risk for the development of neovascularization in retinopathy of prematurity (ROP). In this study, the authors evaluated whether a novel magnetic resonance imaging (MRI) method could be used to identify differences between control retinas and those that will develop neovascularization in the newborn rat model of retinopathy of prematurity (ROP).
METHODS - MRI and a 2-minute carbogen (95% O2/5% CO2) inhalation challenge (see ref. 11) were used to measure noninvasively the change in the posterior vitreous oxygen tension in specific locations across the full extent of the retina in day-12 rats raised in either room air (control, n = 7) or variable oxygen conditions (experimental ROP, n = 7). The experimental ROP animals were examined 2 days before the onset of neovascularization.
RESULTS - In the ROP group, the response to carbogen was lower (P < 0.05) at every distance from the optic nerve than in the control group. Within the ROP group, the vascular midperipheral retinal reaction to carbogen, 1 to 2 mm from the optic nerve, was as low as that from the avascular periphery, 2 to 3 mm from the optic nerve. Although the vascular central retinal response to carbogen, 0 to 1 mm from the optic nerve, was greater than either the vascular midperipheral retina or the avascular periphery in the ROP group, theoretically this difference could be caused by oxygen diffusing from the hyaloidal circulation.
CONCLUSIONS - Carbogen-challenge MRI seems to be a useful tool for assessing the risk of retinal neovascularization in the newborn rat ROP model. This MRI method has potential clinical applicability, for example, because effective laser therapy with retinal sparing may be possible if focal photocoagulation, guided by an MRI map, is performed.