Tears are essential for clear vision and protecting eye health. Researchers discovered that the tears of reptiles and birds are similar to human tears. The results can help scientists understand the tear evolution of various species and develop eye treatments to help with animal conservation.
The collaborative study can be found in the journal Frontiers in Veterinary Science. Professor Arianne Oriá from the Federal University of Bahia, Brazil said that how tears maintain ocular homeostasis is different for every species in various environmental conditions. Their research 'is essential for the discovery of new molecules for ophthalmic drugs,' Oriá said.
Previous tear research has only been gathered from a few mammals such as dogs, horses, monkeys, camels, and humans. Oriá's team just added seven reptile and bird species to the list.
A previous study analyzed the teardrops of five camels from Saudi Arabia. Scientists discovered that camel tears have tiny droplets of oil which act as a lubricant to help them avoid having dry eyes in the desert. The camel tears were better quality compared to the eye lubricant Refresh Plus.
For humans, tears lubricate and protect the eye from harmful environments such as fumes, cutting an onion, and other irritants. Alongside eyelashes, tears also protect the eyes from debris and are naturally antibacterial.
Animal Tears
The tear structure of birds and reptiles are slightly different, explained Oriá, but have similar compounds such as electrolytes in human tears. The crystal structures are also organized differently to guarantee the eye health and equilibrium of species according to the environment they live in.
Several animals like owls, eagles, macaws, caimans, tortoises sea turtles and others were chosen from healthy animals in a wild animal care center. Some species also belonged to a commercial breeder that are kept as pets to help conserve them.
The tear collection was a part of their normal routine check-up. The animal tears were compared to the tears of ten human volunteers. Tears are typically composed of protein, chloride, iron, sodium, and other compounds.
Electrolytes were commonly found in the tears of all species with birds and reptiles having higher concentrations than mammals. The team also measured higher levels of protein and urea in the tears of owls and sea turtles.
Dried tears or crystals can also help researchers discover eye diseases of different species. For example, low levels of urea from tear fluid is normally associated with dry-eye syndrome.
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Conservation of Species
Although mammal, bird, and reptile tears had similar compositions, there were significant contrasts in crystallization patterns of dried tears. Caiman, a reptile closely related to crocodiles, and turtle tears were particularly unique, noted the authors, most likely due to their aquatic environment.
Oriá and the researchers hope to expand their studies to a wider range of species to help with needed eye treatments. Tear evolution can also help with the conservation of animals, especially endangered species, said Oriá.
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