New quantitative analysis, using high-resolution images, of oxygen-induced retinal neovascularization in mice.

Oxygen-induced retinopathy (OIR) has been widely studied as an animal model of retinal neovascularization diseases. Evaluation using this model is mainly performed by counting cell nuclei above the internal limiting membrane in serial cross-sections or by scoring in flat-mounted retinas. Quantitative evaluation is important for accurate elucidation of pathological conditions and the drug evaluations. We therefore attempted quantification using new imaging software and high-resolution images taken with a high-resolution CCD camera. Neonatal mice were exposed to 75% oxygen from postnatal day 7 (P7) to P12, then returned to room air until P17. At each evaluation time, mice were perfused with fluorescein-dextran, and flat-mounted retinas were prepared. Total images of the retinal vasculature were collected and analyzed using the imaging software. P17 normal retinas showed increases in computerized total tube area, total tube length, number of segments, and number of branch points (versus P7 normal retinas). These increases coincided with the development of the retinal vasculature between P7 and P17. P17 OIR retinas similarly showed increases in those parameters, and the number of nodes (thick regions exceeding the maximum width of the vessel) and the node area (abnormality induced by OIR) were markedly increased (versus P17 normal retinas). Accordingly, this approach is considered most suitable for evaluating the number of nodes and node area in this model. Quantification using the present imaging software should be useful for evaluating physiological and pathological neovascularizations in this OIR model.