Prior studies have documented the intertwined developmental courses of retinal blood vessel tortuosity (in fundus photographs)
and retinal dysfunction (in electroretinographs) in Sprague–Dawley rat models of retinopathy of prematurity (ROP). Two such
models, the “50/10 model” and the “75 model,” are named after the oxygen regimens used to induce retinopathy and are characterized
by distinct neurovascular courses that span a range of disease severity. In this study of 50/10 and 75 model rats, retinal
flatmounts were used to study the full vasculature at postnatal day (P) 15, P19 and P30. In addition, the layers of the neural
retina were measured in toluidine blue-stained cross sections. Finally, gross anatomic features of the eye, including axial
length, retinal surface area, and the ratio of anterior to posterior axial-lengths were evaluated. Both clock hours of neovascularization
(NV) and percent avascular retina (AR) peaked at P19 and resolved by P30. Through P19, NV was found in every 50/10 model rat,
but in only 60% of 75 model rats. AR was positively related to NV. All inner layers of the retina (outer plexiform layer through
ganglion cell layer) were attenuated in 50/10 model rats but, in the 75 model, no layer differed significantly from that in
controls. The eyes in both ROP models were smaller than those of age-matched controls. The ratio of anterior to posterior
axial-lengths ranged from 0.45 in controls through 0.37 in the 75 model to 0.32 in the 50/10 model. Thus, eye growth is altered
in these rat models of ROP.
Keywords Retinopathy of prematurity - Rat - Angiogenesis - Anatomy - Refractive development - Histology - Retina