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PURPOSE - To test the hypotheses that, in the newborn rat model of retinopathy of prematurity (ROP), the hyaloidal circulation is functionally impaired and its development is not well coordinated with that of other ocular structures.
METHODS - The functional response of the hyaloidal circulation to a carbogen inhalation challenge was noninvasively evaluated using magnetic resonance imaging (MRI) in day 12 rats raised under either variable oxygen conditions (experimental ROP, n = 8) or room air (control, n = 8). A similar MRI examination was performed in separate experiments using either day 18 newborn control rats (n = 3) or adult rats (n = 9). For each experiment, the hyaloidal circulation perfusion response to carbogen, the functional spatial extent of the hyaloidal circulation in vitreous, and the volumes of vitreous and lens were estimated from MRI enhancement maps.
RESULTS - The hyaloidal perfusion response to carbogen breathing in the newborn rats decreased as follows: control day 12 > experimental day 12 > control day 18; no measurable hyaloidal function was found in the adult rat. Regression analysis indicated a relatively poorer superior-inferior correlation in the temporal response to carbogen inhalation for the experimental animals than in the control newborn rats. The vitreous volume decreased in control rats as expected (adult rat > day 18 > day 12). Good agreement was found between the MRI-determined adult rat vitreous volume (56 +/- 2 microliters) and that of previous reports. Functional hyaloidal volumes during carbogen breathing were not significantly different (P > 0.05) between day 18, day 12 control, and experimental newborn rats. The ratio of this functional hyaloidal circulation extent volume to vitreous volume was significantly different (P < 0.05) between these groups. Covariance analysis revealed a relatively less coordinated development between the functional hyaloidal volume and the vitreous volume in experimental animals than in age-matched control animals, whereas there was coordinated evolution of the hyaloidal circulation and the lens in all the animals.
CONCLUSIONS - Carbogen-enhanced MRI appears to be a powerful new and noninvasive approach for assessing the functionality of the hyaloidal circulation (that is, its ability to respond to a carbogen challenge) and quantitatively comparing the functional hyaloidal extent to other ocular volumes in the same eye during development and during the disease process. Evidence is presented here for the first time that supports the authors' hypotheses that the function of the hyaloidal circulation in experimental ROP is impaired and that the growth of ocular components are less coordinated.