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Studies have been done on the tears of many mammals, but until now, those of birds and reptiles were hardly known, and it turns out that they are very similar to those of humans.
Tears play an important role in maintaining healthy vision in all species, but studying them 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.
A team of scientists from Brazil had managed to analyze the composition of these fluids in mammals such as dogs, horses, monkeys or camels, but wanting to extend the study to other species, the collection of tears was a complex task. Birds and reptiles required special handling.
In a new job, published in the magazineFrontiers in Veterinary Science, the same research team, led by Arianne P. Oriá, from the Federal University of Bahia in Salvador (Brazil) finally managed to extract secretions from seven species of reptiles and captive birds 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.
The results show that these fluids in birds and reptiles are not that different from human tears. It has a similar ionic balance, especially in the gradient of tear electrolytes (components of this fluid) such as sodium and chloride when compared to human tears.
Differences from human tears
After measuring the biochemical composition of these fluids, the authors observed differences in the crystals that formed when the tear fluid was 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 tear fluid and from the migration of macromolecules and proteins to the crystal edges in humans.“Says Oriá, who was surprised by the crystals of the tears of sea turtle and caiman. "They were particularly unique, probably as an adaptation to their aquatic environments.“, He emphasizes.
Thanks to this crystallization pattern, researchers could discover certain types of eye diseases, as well as other variations between types of tears. The analysis of its composition will also help the diagnosis of diseases of the ocular surface.
“Vision is the most important sense for many animal species, and eye diseases can cause them to change their social and eating behaviors, as well as their ability to escape predators.", Concludes the researcher.