Comparative Analysis of Tear Composition in Humans, Domestic Mammals, Reptiles, and Birds

Abstract

Tears are an important component of the ocular surface protection mechanism and are in close contact with the corneal epithelium and the environment. Their composition is well-known in humans; however, there are few investigations on the composition and function of tears in reptiles, birds and others mammals, which would elucidate the mechanisms governing the maintenance of ocular homeostasis. In this work, electrophoretic profiles and an evaluation of total protein, albumin, urea, glucose, and cholesterol concentrations in tears of semi-aquatic, terrestrial, and marine reptiles (Caiman latirostris, Chelonia mydas, Caretta caretta, Eretmochelys imbricata, Lepidochelys olivacea, and Chelonoidis carbonaria), birds (Tyto furcata, Rupornis magnirostris and Ara ararauna), and mammals (Equus caballus and Canis lupus familiaris) were apresented. Human tear components and respective blood serum samples were used as references. The electrophoretic analysis revealed similarities whithin same Classes. The results of the tear-blood serum relationship and the comparison to human tear components showed particularities that are potentially derived from a homeostatic response to the environment. When the tear compositions of animals belonging to different ecological clusters were compared, marked differences were observed in total protein and urea concentrations. Thus, reptile, bird, and mammalian tears are complex fluids with differing concentrations of biochemical components that are potentially a result of the animals' adaptation to different environments.

Comparison of Electrolyte Composition and Crystallization Patterns in Bird and Reptile Tears

“…The tear profile of humans and other mammals is similar ( 13 , 24 ), however this similarity is not observed between birds and reptiles ( 23 ). The highest concentrations of proteins were found in the tears of humans, and similar values were reported in previous studies conducted with healthy patients (around 4 to 9 g/dL) ( 13 , 22 ).…”

“…The intrinsic contact of the tear with the environment is common to all vertebrates, however small amounts can hinder the collection process ( 1 , 21 – 23 ). Previous studies in humans, monkeys and dogs showed similar electrophoretic profile when tears were collected through different methods collection.…”

“…Previous studies in humans, monkeys and dogs showed similar electrophoretic profile when tears were collected through different methods collection. The choice of the collection method for each species was based in previous studies on related species ( 11 – 13 , 16 , 19 , 23 ).…”

The proteomics of roadside hawk (Rupornis magnirostris), broad-snouted caiman (Caiman latirostris) and loggerhead sea turtle (Caretta caretta) tears

“…As an example, studies in humans showed differences in the tears of healthy patients and those with systemic diseases, such as kidney disease and diabetes [38,39]. However, in others species, information on the permeability of the lacrimal gland/plasma interface are not available and direct correlations between blood and tear protein composition are scarce [30].…”

“…Similarly, the projections of the corneal epithelium in freshwater and marine animals can be maintained and nourished by tears [ 9 , 29 ]. Indeed, this interface with the environment followed the adaptation process with the objective to maintain homeostasis, osmotic balance and metabolite transport,[ 9 , 11 ] as already showed by previous studies on the tear composition of animals from the same Classes that live in different environments [ 22 , 30 ].…”