TEARS FOR FEARS
Humans, birds and reptiles have similar tears
From an anatomical point of view, we’re pretty different from birds and reptiles, but it turns out that our tears share remarkable similarities.
Tears are not simply made up of water, but contain other substances like sodium, calcium, urea, chloride and proteins. While tears play an important role in eye health, until now they had only been analysed in a few mammal species. A team led by Prof Arianne Oriá, from Brazil’s Federal University of Bahia, wanted to get a better picture of how tears work in other animals, so they studied various reptile and bird species, including macaws, owls, hawks, a type of parrot, caimans, tortoises and sea turtles.
“Although birds and reptiles have different structures that are responsible for tear production, some components of this fluid are present at similar concentrations as what is found in humans,” said Oriá.
The researchers found that all the bird and reptile tears had similar amounts of electrolytes to human tears, but the owl and sea turtle tears contained higher levels of urea and protein. After studying the tear composition, the team allowed the tears to dry out and studied the crystallisation patterns that formed. These patterns can be used to detect certain eye diseases, along with other variations in the tears. Surprisingly, although the tears all showed similar compositions, the crystals displayed more variety. The caiman and sea turtle tears were particularly unique, which may be an adaptation to keeping the eyes healthy in the reptiles’ watery habitats.
Further research in this field could help boost our understanding of tear types, and therefore lead to improved treatments for animals and humans to optimise eye health.
“This knowledge helps in the understanding of the evolution and adaption of these species, as well as in their conservation,” said Oriá.