(CNN)Birds and reptiles may not resemble humans in many ways, but they cry similar tears.
The composition of human tears is well known, but until now, there was very little research into the composition and structures of tears in reptiles, birds and other mammals.
That lack of research could be considered a crying shame since understanding the makeup of various species' tears can give insight into better eye treatments for both people and animals, as well as improve our understanding of animals' evolutionary adaptations, according to a new study in Frontiers in Veterinary Science.
Researchers in Brazil collected samples of healthy animals' tears from seven species of birds and reptiles, including macaws, hawks, owls and parrots, as well as tortoises, caimans and sea turtles.
"It's important to understand healthy animals in order to treat sick animals, because species depend on their vision," said lead study author Arianne Oriá, a professor of clinical veterinary medicine at the Federal University of Bahia in Salvador, Brazil. "Animals are not able to live without vision in the wild. A sea turtle without vision will die."
Humans also need to 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 possibly even more severe vision problems.