Structure of the lid margin in laboratory animals

Abstract

Abstract Purpose The eye lid margin is of great importance for the spreading and the limitation of the tears. The so called lid wiper which is a specialized zone at the inner lid border directly apposed to the corneal surface for spreading the preocular tear film has, at present, only been described for the human conjunctiva. We have investigated common laboratory animals (rat and rabbit) for the presence of such a zone. Methods Conjunctival whole‐mount specimens and total bulbi were investigated by serial section histology in ten rats (DA and Lewis) and in ten rabbits (NZW and Chinchilla). Results The stratified squamous keratinised epidermis of the free lid margin showed a sharp transition with loss of the keratin layer at the level of the meibomian glands. Close to the inner lid border it was replaced by a small zone of an optically denser epithelium covered by para‐keratinised cells. This area represented the mucocutaneous junction (MCJ) equivalent to the line of Marx in the human.The MCJ rapidly transformed into a thickened 8‐12 cell layered stratified epithelium of that formed a cushion‐like epithelial elevation, reclined sharply towards the inner lid border and hence formed a typically relatively sharp lip‐like edge. The lid‐wiper epithelium showed species‐specific differences in morphology (cuboidal with goblet cells in the rabbit versus squamous without goblet cells in the rat) but it extended all along the lid margin in both species. Conclusion At the inner border of the upper and lower lid of rat and rabbit, several zones of different morphology occur similar to the human including a lid‐wiper structure. Since lid wiper epitheliopathy was shown as a sensitive early indicator for human dry eye syndrome its investigation may be useful for future research in dry eye models of laboratory animals.