Abstract

Our purpose was to identify and histologically characterize the tear producing glands of pinnipeds. Following humane euthanasia for unrelated reasons, dissection was performed to identify structures consistent with glandular tissues. Entire eyelids, third eyelids, globes and orbital contents were excised and fixed in 10% buffered formalin. Samples were processed for histological evaluation and stained with hematoxylin and eosin. The lid consisted mainly of muscular tissue. Two large glands were identified, one at the base of the nictitans and the other beneath the dorsotemporal superior eyelid. These were identical histologically, with a tubuloacinar arrangement and a seromucinous secretory apparatus. We previously reported that pinnipeds have sebaceous glands at the eyelid margin, but are different in size and orientation compared to terrestrial mammal meibomian glands, consistent with the observation that these animals lack a lipid layer typical of land mammals. In the absence of lipid, aqueous and mucous components of the tear film may play a greater role in protection of the eye. The aqueous layer is likely produced by the lacrimal glands in the superior eyelid and beneath the nictitans, similar to terrestrial mammals.