The differences in the eyelids microstructure and the conjunctiva‐associated lymphoid tissue between selected ornamental and wild birds as a result of adaptation to their habitat

Abstract

The aim of the study was to describe the morphology of the upper, lower and third eyelid and characterize the organized lymphoid follicles and diffuse lymphocytes from ornamental and wild birds. The goal of these examinations was also to identify avian conjunctiva‐associated lymphoid tissue (CALT) and lymphoid tissue that contained specialized high endothelial venules. The upper, lower and third eyelid from 30 species of ornamental and wild birds representing 21 families were examined under light microscopy and using scanning electron microscopy. The third eyelid in all of the examined birds was composed of a free margin, which was divided into two parts. The largest tarsal plate of the third eyelid was observed in the greater rhea (Rheimorphae), the white‐tailed eagle and steppe eagle (Accipitrimorphae) and was approximately 13–15 mm wide and 9–11 mm long, respectively. In all of the examined birds, the CALT was associated with a rich network of small vessels. In addition, the presence of characteristic high endothelial venules and roundish bright endothelial cells was confirmed in the upper and lower eyelids or only in the lower eyelid (Phoenicopterimorphae, Procellariimorphae and Strigimorphae).

Anatomical and morphometric evaluation of the orbit, eye tunics, eyelids and orbital glands of the captive females of the South African painted dog (Lycaon pictus pictus Temminck, 1820) (Caniformia: Canidae)

“…In contrast, the presence of lymphatic cells in the lamina propria of the eyelids was found in the crab-eating fox [21]. It was not reported whether they were typical CALT conjunctival lymphoid nodule agregates, intraepithelial lymphocytes, subepithelial lymphoid cells or diffuse lympocytes adjacent lymphatic and blood vessels, were covered by follicle-associated epithelium (FAE) [81][82][83]. Characteristically, there are no goblet cells in the lymphoid region of the epithelium.…”

“…The precorneal tear film performs many important functions ensuring the correct functioning of the eye. These include maintaining a smooth surface for light refraction, lubrictaing the upper and lower eyelids, conjunctiva and cornea, suppyling the cornea with nutrients and transporting metabolic by-products from the corenal surface, providing leucocytes wtih access to the cornea and conjunctiva, removing foreign materials from the conjunctiva and cornea, defending the ocular surface from pathogens via specific and nonspecific antibacterial substances [81,95]. The tear film consists of the three layers: a superficial oily layer, a central aqueous (serous) layer, and a thin mucous (glycoproteinaceous) layer covering the cornea.…”

“…The first layer is oily and is produced by the tarsal glands, which are commonly known as Meibomian glands. They provide lubrication and a smooth optical surface, they prevent overflow of tears from the lid margins, reduce the evaporation of the underlying aqueous layer (tears) and prevent contamination of the precornael tear film from debris [44,81]. The second layer is the aqueous layer and is a major component of the precorneal tear film.…”

Analysis of the kinetics of the eyelids of little owl Athene noctua

“…They also recorded that the third eyelid is an elastic membrane and moves rapidly. The main purpose of this apparatus is to cleanse and lubricate the front of the cornea, as well as, to act as an immune protection for the eye (Klećkowska-Nawrot et al, 2017). Klećkowska-Nawrot et al (2017) recorded wide variations in the microstructure of eyelids in many wild bird species.…”

“…The main purpose of this apparatus is to cleanse and lubricate the front of the cornea, as well as, to act as an immune protection for the eye (Klećkowska-Nawrot et al, 2017). Klećkowska-Nawrot et al (2017) recorded wide variations in the microstructure of eyelids in many wild bird species. These recent studies confirmed that the eyelids of birds differ in their structure among different avian species.…”