Histological, histochemical and fine structure studies of the lacrimal gland and superficial gland of the third eyelid and their significance on the proper function of the eyeball in alpaca (Vicugna pacos)

Abstract

The lacrimal gland (LG) and superficial gland of the third eyelid (SGTE) belong to accessory organs of the eye. The aim of the present studies was to evaluate the histological, histochemical and fine structure of the LG and SGTE obtained from 3 adult females and 2 adult males of alpaca (Vicugna pacos). The LG was situated in the dorsolateral angle of the orbit between the dorsal rectus and the lateral rectus muscles. The SGTE was located between the medial rectus muscle, the ventral rectus muscle and was partially covered by the ventral oblique muscle of the eyeball. There were no effect of gender on the morphometry of examined LG and SGTE. The third eyelid resembles an anchor in shape. During histological and ultrastructural analyses using light and transmission electron microscopy, it was established that the LG and SGTE are tubulo-acinar glands with mucoserous characters. The LG contains either lymphocytes or plasma cells, while SGTE had rare plasma cells and numerous lymphocytes in connective tissue. The cartilage of the third eyelid was composed of hyaline tissue. Numerous aggregations of lymphocytes as lymph nodules in bulbar surface of the third eyelid were observed. The LG and SGTE secretory cells exhibited a similar ultrastructure appearance in electron microscopic examination, with secretory cells tightly filled with intracytoplasmatic secretory granules and numerous clusters of mucus of different sizes which were observed in the peripheral cells compartment.