Variations in Retinal Nuclear Areas in a Neonatal Mouse Model of Retinopathy of Prematurity by Histopathology

Abstract

Purpose: Premature infants requiring supplemental oxygen are at risk of developing retinopathy of prematurity (ROP) and retinal structural and vascular abnormalities. The purpose of the current study is to investigate changes in retinal cell density in an oxygen-induced retinopathy (OIR) mouse model of ROP by quantitative analysis of ex-vivo histological slides.

Methods: Histological slides of the retina were obtained from enucleated eyes of OIR C57BL/6J mice (N = 6 eyes) and control mice (N = 6). OIR mice were exposed to 75% oxygen from post-natal day 7 (P7) to P12 before returning to room air, while control mice were exposed to room air continuously. Mice were sacrificed at P17-P19, the eyes enucleated, and histological slides stained with hematoxylin and eosin. The areas of the cell nuclei in the retinal inner nuclear and ganglion cell layers (inner retinal area) and in the retinal outer nuclear (outer retinal area) were quantified using a semi-automated morphometric image analysis software (Motic). These areas were divided by the total area of a selected region of the retina.

Results: The relative inner retinal area in OIR mice (14 ± 1%) and control mice (15 ± 1%) were similar (p = 0.2). Likewise, there was not a statistically significant difference in the outer retinal area in OIR mice (26 ± 2%) and control mice (23 ± 4%) (p = 0.2). In both control and OIR mice, the outer retinal area was significantly greater than the inner retinal area (p < 0.001). The sum of the inner and outer retinal areas in OIR mice (40 ± 2%) and control mice (38 ± 5%) was similar (p = 0.4). The ratio of the outer to inner retinal areas was significantly higher in OIR mice (1.9 ± 0.1) than control mice (1.6 ± 0.3) (p = 0.04).

Conclusions: In OIR mice, there was an increased proportion of outer to inner retinal nuclei, as compared to control mice. This may reflect variations in vascular supply and metabolic needs. Study of retinal structural changes may aid the understanding of ROP pathogenesis.

Keywords: 688 retina • 706 retinopathy of prematurity • 698 retinal development