Bird and reptile tears are very similar to human tears

A new study published by Frontiers has revealed that bird and reptile tears are very similar to human tears. The research provides new insight into the evolution of tears, and may ultimately lead to improved treatments for eye disease.

Study first author Professor Arianne P. Oriá is an associate professor of Veterinary Sciences at the Federal University of Bahia in Brazil.

“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,” said Professor Oriá.

Across species, tears play a very important role in maintaining healthy eyesight. Prior to the current study, however, tears had been studied in very few species beyond humans.

Professor Oriá’s team has now analyzed tears from 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,” explained Professor Oriá. 

“But the crystal structures are organized in different ways so that they guarantee the eyes´ health and an equilibrium with the various environments.”

The researchers collaborated with

veterinarians from wild animal care centers and a commercial breeder to collect tear samples from healthy, captive animals. 

The team compared tears from 10 healthy human volunteers to those of macaws, hawks, owls, parrots, sea turtles, and other animals. 

The detailed analysis of tear composition revealed that all of the tear types contained similar levels of electrolytes such as sodium and chloride, even though these levels were slightly lower among human tears.

In addition, owls and sea turtles had greater concentrations of urea and protein in their tears. 

The researchers also examined the crystals that formed when the tear fluid dried out. This crystallization pattern can be used as an indicator of certain types of eye disease.

All of the different species had similar tear composition, but the experts were surprised to find that the crystals showed more variation. 

Sea turtle and caiman tear crystals were extremely unique, which is probably the result of adaptation to their specific environments.

Further research that involves  additional species is needed to expand our knowledge of tears and treatments for eye diseases.

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

The study is published in the journal Frontiers in Veterinary Science.

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By Chrissy Sexton, Earth.com Staff Writer