Although the tears of many mammals have been studied, until now, those of many birds and reptiles, very similar to those of humans, have been hardly known.

Collecting tears from the Brazilian alligator, also known as the alligator overo.

The tears play an important role in maintaining healthy eyesight in all species, but its study in certain animals is not an easy task. These complex fluids present different concentrations of biochemical components that result from the adaptation of different animals to their environments.

Until now, a team of Brazilian scientists had managed to analyze the composition of these fluids in other mammals such as dogs, horses, monkeys or camels, however, in other animals, their collection had been complex. Birds and reptiles require special handling, in addition to being healthy.

In a new work, published in the magazine Frontiers in Veterinary Science, the same research team, led by Arianne P. Oriá, from the Federal University of Bahia in Salvador (Brazil) has achieved extract secretions from seven species of reptiles and birds Captive as pets, or belonging to conservation programs. Macaws, hawks, owls, and one type of parrot, as well as turtles, alligators, and sea turtles add to this exclusive list of animals.

“Discover how tears are able to maintain ocular homeostasis, even in different species and environmental conditions, it is crucial to understand the processes of evolution and adaptation, and it is essential for the discovery of new molecules for ophthalmic drugs ”, says Oriá.

The results show that these fluids in birds and reptiles they are not so different from human, that is, they show similarities in their ionic balance, especially in the gradient of tear electrolytes (components of this fluid) such as sodium and chloride when compared to human tears.

“Although birds and reptiles have different structures that are responsible for the production of tears, some electrolytes are present in concentrations similar to those found in humans,” explains the researcher. “But lCrystalline structures are organized in different ways to guarantee the health of the eyes and the balance with the different environments ”, he continues.

Differences from human tears

After measuring the biochemical composition of these fluids, the authors observed differences in crystals that formed when tear fluid dried. These showed more variation compared to the tears of the ten human volunteers who participated in the study.

“Crystallization is derived from the electrolytes that form the tear fluid and from the migration of macromolecules and proteins to the edges of the crystals in humans”, points out to SINC Oriá, who was surprised the crystals of the tears of sea turtle and alligator. “They were particularly unique, probably as an adaptation to their aquatic environments,” he stresses.

Thanks to this crystallization pattern, researchers could discover certain types of eye diseases, as well as other variations between the types of tears. The analysis of its composition will also help the diagnosis of diseases of the ocular surface.

“The vision is the most important sense for many animal species, and eye diseases can make them change their social and eating behaviors, as well as their ability to escape predators “, concludes the researcher.