The Role of the Ocular Lids of the Black-Winged Kite, Elanus caeruleus ,
in the Immune Protection of the Eye
Abstract
The aim of the study was to describe the morphological features and
microstructure of the upper, lower, and third eyelids of black-winged
kite, Elanus caeruleus, as well as characterize the organized
lymphoid follicles and lymphocytes in the eyelid’s mucosa, and to
illustrate the importance of the eye adnexa in the eye’s immune
protection. The black-winged kite has large forward-facing eyes placed
under a bony shelf (lacrimal process) that shaded them. Both eyelids
have thick and pigmented edges and bear two rows of long and finely
modified filoplume feathers that increase at the anterior canthus. It
was found that the lower eyelid appears longer and thinner than the
upper one, as well as having sparse feathers on the skin surface of the
lower eyelid but lack on the upper. The third eyelid is a white opaque
membrane moving obliquely over the cornea surface. The melanocytes
appear in the stratum basal of upper and lower eyelids and the
Langerhans cells were observed within the layers of stratum spinosum,
near the feather follicle and around the blood vessel. Aggregations of
lymphatic cells were present under the conjunctival epithelium within
the stroma of the lower eyelid (in the orbital zone near the tarsal
plate), while absent in the upper eyelid and nictitating membrane. The
present study revealed that many high endothelial venues (HEV) are
distributed along the lower eyelid and increase in the palpebral
marginalis, while in the upper eyelid, it is restricted in the marginal
region. The density of goblet cells on the conjunctiva surface of the
upper eyelid and the nictitating membrane is higher than that of the
lower eyelid. The leading edge and bulbi surface of the third eyelid
reveal the irregular surface of the apical cell, with many cilia having
variable amounts of secretory vesicles as shown by TEM.