Pigment Deposition in the Rat Retina

Incidental findings in the rat eye are not uncommon in acute and long-term toxicological studies. These findings can be associated with a number of causes unrelated to treatment with the test article, including congenital malformation, trauma, infection, metabolic disease, genetic predisposition, and age-related changes. The occurrence of pigment deposition in the retina of Wistar Hannover (Crl:WI (Han)) rats in a 4-week toxicity study is reported in this communication. The microscopic examination of the eyes in the 4-week toxicity study revealed focal yellow-brown pigment deposits in the retina, mainly located in the ganglion cell layer. The retinal pigment deposits were randomly distributed in the control and treated groups and were considered incidental. The deposits were clearly positive for ferric iron in the Perls' stain but not for lipofuscin by the Schmorl's and Long Ziehl-Neelsen methods. The iron-containing pigment is likely to represent hemosiderin accumulation after retinal micro-hemorrhage or could be indicative of the normal intraretinal iron transport and turnover.