Spontaneous Intraocular Hemorrhage in Rats during Postnatal Ocular Development

To study spontaneous intraocular hemorrhage in rats during postnatal ocular development and to elucidate the underlying mechanism, postnatal ocular development in the albino Wistar Hannover (WH) and Sprague–Dawley (SpD) and pigmented Long–Evans (LE) strains was analyzed. Pups (n = 2 to 5) from each strain were euthanized daily on postnatal days (PND) 0 through 21 and their eyes examined macroscopically and histologically; similar analyses were performed in 26 to 39 additional WH pups daily from PND 7 to 14. At necropsy, ring-shaped red regions and red spots were present in the eyes of WH and SpD rats. These lesions were attributed histologically to hemorrhage of the tunica vasculosa lentis or of the retina, choroid, and hyaloid artery, respectively. Similar intraocular hemorrhages occurred in LE rats, although the macroscopic alterations found in WH and SpD rats were not present in this strain. Among the 3 strains evaluated, the incidence of the intraocular hemorrhage was highest in WH rats. We here showed that intraocular hemorrhage occurs spontaneously during normal ocular development in rats regardless of the strain; however, the region, degree, and incidence of intraocular hemorrhage differ among strains. Hemorrhage in the tunica vasculosa lentis and hyaloid artery may result from the leakage of erythrocytes from the temporary vasculature of these tissues during regression. The mechanisms underlying hemorrhage in the retina and choroid remain unclear. To our knowledge, this report is the first to describe the spontaneous intraocular hemorrhage that occurs during postnatal ocular development in rats.