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Macaws (top left) don’t like to have an eye exam. They completely refuse to do it after lunch!

You won’t win a staring contest with a caiman (top right). Its tears are so  thick that it only needs to blink once every few hours.

Rabbits’ (bottom left) tears are super stable to help them keep still and hide from predators. A blink at the wrong time could mean the difference between life and death.

Snakes (bottom right) like the bush viper  have a clear skin film called a spectacle that holds tears against their eyes.

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STANDARDS

CCSS: 6.SP.B.5.B, MP1, MP3, MP5

TEKS: 6.12A

Measuring Tears

What have scientists learned by studying animal tears?

She doesn’t make animals cry for her work, but Arianne Pontes Oriá does study their tears! The Brazilian veterinarian carefully collects an animal’s tears—from owls to crocodiles—and places them on microscope slides. Under magnification, each animal’s tears look like a snowflake, revealing their unique structure. Studying this structure helps Oriá understand these adaptations, including how some animals can go so long without blinking.

Only humans cry to express emotion, but all animals have tears. Tears are essential to keep eyes healthy because they protect the cornea, the clear outermost part of the eye. The watery substance contains proteins, salts, and oxygen that nourish the cornea. Normally blood provides nutrients and oxygen to cells, but there are no blood vessels in the cornea. Blinking helps spread tears across the eye, keeping it clean and moist.

“Different animals have a different stickiness to their tears,” says Sara Thomasy. She’s an animal ophthalmologist who studies and treats animal eyes. If a crocodile’s tears weren’t so thick, for example, they would wash away in the swampy water.

She doesn’t make animals cry for her work. But Arianne Pontes Oriá does study their tears! The Brazilian veterinarian carefully collects the tears of animals from owls to crocodiles. She places them on slides and examines them under a microscope. Up close, each animal’s tears have a unique structure. Studying them helps Oriá understand how different types of tears help animals survive.

Only humans cry to express emotion. But all animals have tears. Tears keep eyes healthy by protecting the cornea, the clear outer part of the eye. Most cells in the body get the nutrients and oxygen they need from the blood. But there are no blood vessels in the cornea, so tears provide nourishment instead. Blinking helps spread tears across the eye, keeping it clean and moist.

“Different animals have a different stickiness to their tears,” says Sara Thomasy. She’s veterinarian who studies and treats animal eyes. A crocodile’s tears are very thick, for example. If they weren’t, they would wash away in the swampy water where crocodiles live.

Some animals, like snakes, live in dry environments and need extra-moisturizing tears to keep their eyes from drying out. Others, like rabbits, freeze in place to hide from predators. So they need to go for long periods of time without blinking. “Rabbits have a tear film that’s so stable that they only have to blink every half an hour,” says Thomasy.

When researchers collect tears, expert animal handlers restrain the creature. Then the scientists either swab the animal’s eyes or extract the tears using a soft syringe. For some species, it can take more than six months to collect 1 milligram of tears!

“We can use what we learn about animals to help people,” says Thomasy. “It’s very painful when your eye doesn’t produce enough tears. We could find a whole new way to treat dry eye by studying species who have adaptations.”

Some animals, like snakes, live in dry environments. They need moisturizing tears to keep their eyes from drying out. Others, like rabbits, hold very still to hide from predators. That means they need to go a long time without blinking. “Rabbits have a tear film that’s so stable that they only have to blink every half an hour,” says Thomasy.

Collecting animal tears takes a careful process. First, expert handlers hold the animal still. Then scientists use a swab or soft syringe to extract tears from the animal’s eyes. They repeat this over time to gather enough tears to study. It sometimes takes more than six months to collect just 1 milligram!

“We can use what we learn about animals to help people,” says Thomasy. For instance, people’s eyes sometimes don’t produce enough tears. This painful condition is called dry eye. “We could find a whole new way to treat dry eye by studying [these] species,” she says. 

Read the research scenarios and determine which type of graph would be best for displaying the data the scientists collect. Record your work and answers on our answer sheet.

Read the research scenarios and determine which type of graph would be best for displaying the data the scientists collect. Record your work and answers on our answer sheet.

Oriá analyzes the different proteins in a caiman’s eye. Each type of protein makes up a different part of the total proteins in its eye. Which graph should she use to display this data?

Oriá analyzes the different proteins in a caiman’s eye. Each type of protein makes up a different part of the total proteins in its eye. Which graph should she use to display this data?

A researcher records the number of times different animals blink over the course of 5 minutes. Which graph should she use to display this data?

A researcher records the number of times different animals blink over the course of 5 minutes. Which graph should she use to display this data?

Thomasy collects rabbit tears at the same time every day for one month, and records each day’s tear volume. Which graph should she use to display this data?

Thomasy collects rabbit tears at the same time every day for one month, and records each day’s tear volume. Which graph should she use to display this data?

A. Oriá wants to create a set of graphs that compare the composition of human tears to barn owl tears. Which type of graph should she use to display this data?

A. Oriá wants to create a set of graphs that compare the composition of human tears to barn owl tears. Which type of graph should she use to display this data?

B. Is there another way to represent this data? Explain.

B. Is there another way to represent this data? Explain.

What type of data would a researcher need to collect to make a line graph representing the tear production of a hawk? Explain.

What type of data would a researcher need to collect to make a line graph representing the tear production of a hawk? Explain.

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