Retinal folding in the term rabbit fetus—Developmental abnormality or fixation artifact?

Preclinical reproductive toxicology studies must be performed to provide information on the risk of causing fetal harm in pregnant patients. These studies detect fetal malformations, which may or may not be drug-related adverse events. In the rabbit fetus, “slight retinal folding” is commonly observed; there is anecdotal evidence that these folds may be caused by routine (Bouin’s fluid) fixation. This study used magnetic resonance imaging (MRI) to assess rabbit retinal architecture in fresh specimens, which was then reassessed following Bouin’s fluid fixation. A total of 30 fetuses from 5 litters were imaged. No retinal folding was detected in fresh specimens but it was observed in a majority of fetuses post-fixation. The use of Davidson’s fixative followed by Bouin’s fluid showed a markedly lower incidence of “slight retinal folding”. Conclusion: slight retinal folds in the rabbit fetus are likely artifactual and can be reduced using Davidson’s fixation prior to Bouin’s.