The composition of human tears is well known, but so far, there has been very little research on the composition and structures of tears in reptiles, birds and other mammals.
“It̵7;s important to understand healthy animals in order to treat sick animals, because species depend on their vision,” said lead author Arianne Oriá, professor of clinical veterinary medicine at the Federal University of Bahia in El Salvador. , Brazil. “Animals are not able to live without sight in the wild. 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, tears and the edges of the eyelids. Otherwise they will have a lot of discomfort, redness and itching, or maybe even more severe vision problems.
The new study found both similarities and differences with human tears that may be key to veterinary treatments and eye diseases. Although the tears of mammals like 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 looked at crystallization patterns that form when tears dry out, which can provide insights into variations in tear types and even detect 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 (electrolyte) are present in concentrations similar to those found in humans,” Oriá added in a press release. “But crystal structures are organized in different ways in order to guarantee eye health and a balance with different environments.”
Despite the tear-like composition in the species, surprisingly the crystal structures showed greater variation. The crystal structures in sea turtles and cayman tears were the most unique, likely a product to adapt to their aquatic environments.
Environment is essential
“Tears are the most exposed fluids to the environment. So, with subtle modifications to the environment, tears will be modified,” Oriá explained. “For example, in humans, we know that people who smoke have changed their tears.”
“If we modify our habitat with pollution or something else, we will create an unhealthy habitat for our tear film,” Oric said. “So animals, as well as humans, will have to have many years to adapt to the habitat.”
She added that in many parts of the world, habitats are being polluted and destroyed faster than animals – and humans – can adapt.
Oriá said more research is needed to expand understanding of the tears of more species and to translate those findings into treatments for eye problems in both animals and humans.
“This knowledge helps to understand the evolution and adaptation of these species, as well as their conservation,” Oric said.