The composition of human tears is well known, but so far there has been very little research into the composition and structures of tears in reptiles, birds and other mammals.
“It is important to understand healthy animals in order to treat sick animals, because species depend on their vision,” said lead studio author Arianne Oriá, a professor of clinical veterinary medicine at the Federal University of Bahia in Salvador, Brazil. “Animals are not able to live in the wild without vision. A sea turtle without vision will die.”
People should also have what researchers call a healthy “ocular surface” – the outer layer of the eye, including the cornea, the tears and the edges of the eyelids. Otherwise, they will have a lot of discomfort, redness and itching, or maybe even more severe problems with vision.
The new study found both similarities and differences with human tears that may be key to veterinary treatments and eye disease. Although the tears of mammals such as dogs and horses are more similar to humans, there are similar amounts of electrolyte fluid in the tears of birds, reptiles and humans (but birds and reptiles had slightly higher concentrations than humans).
The researchers also saw the crystallization patterns that form when tears dry out, which can provide insight into variations in file types and even reveal certain types of eye disease.
“Although birds and reptiles have different structures that are responsible for the production of tears, some components of this fluid (electrolytes) are present in similar concentrations as what is found in humans,” Oriá added in a press release. “But the crystal structures are organized in different ways, so they guarantee the health of the eyes and a balance with the different environments.”
Despite similar triangulation across species, the crystal structures surprisingly showed a greater variation. The crystal structures in sea turtles and caimantranes were the most distinctive, probably a product of adapting to their aquatic environments.
Environment is key
“Tears are the most exposed fluids to the environment. So, with subtle adjustments to the environment, the tears will change,” Oriá explained. “In humans, for example, we know that people who smoke have shed their tears.”
“If we adapt our habitat with pollution like anything else, we will create an unusual habitat for our tear film,” Oriá said. “That animals, like humans, will also have to have many years to re-adapt to the habitat.”
She added that in different parts of the world habitats are being polluted and destroyed faster than animals – and humans – can adapt.
Oriá said more research is needed to broaden the understanding of the tears of more species and translate these findings into treatments for eye problems in both animals and humans.
“This knowledge helps in understanding the evolution and adaptation of these species, as well as in their conservation,” Oriá said.
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