Ontogeny of Eyelids in Indian Buffalo (Bubalus bubalis): A Histological Study

The ontogeny of the eyelids involves a coordinated process of cell proliferation, changes in cell shape, migration and cell death. The function of the eyelids is to protect the eye from mechanical and optical injuries. The prenatal development of eyelids has many interesting milestones and events in various animals, as reported. But the information on histomorphogenesis of eyelids in Indian buffalo seems to be meagre. So, the study was planned to observe various microscopic milestones during the prenatal development of eyelids in Indian buffalo (Bubalus bubalis). A total of 33 embryos/foetuses were divided into three groups on the basis of their Crown Vertebral Rump Length (CVRL) viz. Group I (< 20.0 cm), Group II (> 20.0 but < 40.0 cm) and Group III (> 40.0 cm). For the first and second groups, the entire eyeball with its adnexa was collected in 10% neutral buffered formalin, while for the third group, after extirpation of the eyeball, the eyelids were dissected and fixed in 10% neutral buffered formalin. These specimens were then processed for histological sections and observed for microscopy. The first evidence of developing eyelids was observed in a 1.6 cm fetus and it was the development of two buds just anterior to the developing cornea representing upper and lower eyelids. They further grew to join together, resulting in the closure of eyelids at 7.1 cm CVRL, thus the conjunctival sac was closed between the developing cornea (posteriorly) and the fused upper and lower eyelids (anteriorly). The bud of the developing third eyelid was seen as a growth coming out from the base of the upper eyelid at 7.1 cm CVRL, which became prominent in the 8.0 cm CVRL stage fetal eye. At the CVRL 19.5 cm stage, the primordia for the tarsal gland were observed, which were located towards the conjunctival border. A semisolid cellular swelling representing future sweat glands was witnessed at 20.5 and 22.8 cm CVRL stages, and these swellings originated from the proximal third of the developing eyelashes follicle. Whereas, the primordia of sebaceous glands were seen to be developed from the lower third of these eyelashes follicles at the same stages. At 31.0 cm CVRL, the upper and lower eyelids showed well differentiated eyelashes follicles with all the layers except the internal root sheath and the distinct cuticle. During further development of the third eyelid, the formation of a plate of hyaline cartilage was observed in the 27.5 cm CVRL stage, which was surrounded by developing glands of the third eyelid. In the third group foetuses, the eyelids showed a keratinized epidermis with all the layers of skin, increased melanin content, highly developed tarsal glands, well developed eyelashes follicles with all layers and surrounded by sebaceous glands. The third eyelid had well developed skin, a plate of hyaline cartilage and superficial and deep glands. The outer surface of the third eyelid was formed by keratinized stratified squamous epithelium, whereas the bulbar side was lined by the palpebral conjunctiva.