The tears shed by birds and reptiles are surprisingly similar to human tears, according to a new study. However, researchers also identified key differences.

The study, published Thursday in the journal Frontiers in Veterinary Science, also identified key differences and could help scientists better understand the evolution of tears among animal groups.

The findings, researchers say, could help the develop of new ophthalmic treatments for humans and animals.

"Discovering how tears are able to maintain the ocular homeostasis, even in different species and environmental conditions, is crucial for understanding the evolution and adaptation processes, and is essential for the discovery of new molecules for ophthalmic drugs," first author Arianne P. Oriá, an associate professor of veterinary sciences a the Federal University of Bahia, in Salvador, Brazil, said in a news release.

Tears help keep eyes moist and clear of debris. They are essential to healthy vision, but the study of tears has been limited to just a few mammal groups -- humans, dogs, horses, monkeys and camels.

For the last several years, Oriá has been leading an effort to document the tears of other types of animals, including reptiles and birds. Her latest paper offers insights into the tears produced by seven species of birds and reptiles.

"Although birds and reptiles have different structures that are responsible for tear production, some components of this fluid -- electrolytes -- are present at similar concentrations as what is found in humans," said Oriá. "But the crystal structures are organized in different ways so that they guarantee the eyes´ health and an equilibrium with the various environments."

With the help of veterinarians and caretakers at a conservation center and wild animal care center, as well as a commercial animal breeder, researchers were able to collect tears from healthy captive animals, including macaws, hawks, owls, parrots, tortoises, caimans and sea turtles.

When scientists analyzed the chemical composition of the tears, they found levels of electrolytes, such as sodium and chloride, similar to those found in human tears. The researchers measured slightly higher levels of urea and protein, however, in the tears of owls and sea turtles.

Researchers also studied the crystals that form as tears dry out. In addition to pinpointing differences in tears, crystallization patterns can also reveal the presence of different eye diseases.

Despite the similarities in chemical composition, the tears of the different birds and reptile species showed a surprising amount of variation, the researchers said.

The crystallization patterns observed in the tears of sea turtles and caimans were especially unique -- they must produce special tears to protect their eyes underwater.

The researchers said they plan to continue collecting and studying the composition of the tears produced by a wider and wider variety of animal species. In the future, scientists hope to study tears produced by wild animals.

"This knowledge helps in the understanding of the evolution and adaption of these species, as well as in their conservation," said Oriá.

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