Computerized digital image analysis of retinal vessel density: application to normoxic and hyperoxic rearing of the newborn rat.

Because of the inherent nature of existing techniques for vascular assessment of the retina, quantitative rigor has been difficult to attain. Computer imaging has now made possible measurement of oxygen-induced alterations in retinal blood vessels that is precise, accurate and repeatable. Newborn rats were exposed to 80% oxygen for 14 days as an animal model for retinopathy of prematurity (ROP). Ink perfusion, followed by retinal dissection, yielded silhouettes of the retinal vascular network. These images were digitized and enhanced by the MegaVision 1024XM imaging system in order to facilitate measuring extent of vasculature and capillary density. Mean grey levels, or 'mu', were 33.1 +/- 3.4 and 20.1 +/- 3.5 for room air- and oxygen-reared rats, respectively. These values are directly proportional to the fraction of the overall image that is vascular material, and, therefore, describe the extent of vaso-obliteration resulting from the oxygen exposure. The values were subsequently converted to square millimeters of vessel area to facilitate comparison to past and future studies. Oxygen rearing does not effect retinal area, but decreases retinal artery and vein diameter and decreases the linear extent of vessels toward the retinal periphery.