Strange children have 'dolphin eyes'

Unlike ordinary people, the children of a Thai tribe can see clearly below the waves - how can they do that, and can that ability be learned?

"The rising tide is also the time when the children start swimming. But it is not the same as what I saw. They dive under the water, their eyes are wide - like little dolphins."

Deep in the archipelago in the Andaman Sea, along the west coast of Thailand there is a small tribe called the Moken , or marine nomads . Young children here spend most of the day in the sea, diving for food. They are very suitable for this job - because they can see underwater. And just a little practice, their special eyesight can be obtained on any young person.

In 1999, Anna Gislen of Lund University, Sweden, while studying different aspects of vision, was suggested by her colleagues about the special sense of the Moken tribe . "I was sitting in a dark lab for three months, so I thought," Oh yeah, why not go to Asia instead of sitting here " , " Gislen said.

The adult of this tribe will lose the special eyesight they had when they were young.

Gislen and her six-year-old daughter traveled to Thailand and immersed themselves in the Moken community, who live in houses on the pole. When the tide came, the Moken children swam into the water, diving down to find food that was a few meters below the point that Gislen and her daughter could see clearly."Their eyes widen, hunt for oysters, snails, and sea cucumbers, without difficulty , " she said.

Gislen did a test to see how well the kids' underwater vision was. The children were very excited to participate, Gislen said: "They think it's just a fun thing."

The Moken live in islands on the Andaman Sea and along the west coast of Thailand.

Children will dive into the water and head their heads to a board. From there they will see a straight line displayed horizontally or vertically. Once they see, they will return to the water surface and announce which direction the line goes. Each time you dive, the straight line will be thinner, the more difficult the task is. And the young Moken may look twice as good as the European children in the same experiment done later.

What is happening? To see clearly on land, light entering the eye needs to be refracted onto the retina. The retina is located at the back of the eye and contains specialized cells, converting light signals into electrical signals for the brain to perform into images.

Light is refracted when it enters the human eye because the cornea in addition to water, which is denser than air outside the eye.

With Moken children's special vision training, it can be obtained on any young person.

When the eye in the water, which has the same density as the cornea, loses the ability of the cornea to refract, making the image blurry.

Gilsen figured out that in order for the Moken children to see clearly in the water, they would either have to adapt to change the way their eyes operate under water, or they would learn to use other eyes to go underwater.

The first idea seems impossible, because changing the structure of the eye means that they will not be able to see clearly when on land. A simple eye test proved this - the Moken child, when he looked clearly on the ground, was just like other children of his age.

Obviously it must be some kind of eye correction, Gislen thought. There are two ways you can enhance underwater vision in theory. You can change the shape of the lens - also known as vision correction - or you can make the pupil smaller, causing the field to increase.

It was also possible that Moken's eyes were adapted to seawater, and avoided being stimulated by salt.

The size of the pupil is easy to measure - and it turns out they can shrink the pupil to the maximum limit of humans. But this alone cannot fully explain why they have such eyesight. This makes Gislen believe that regulating eyesight also contributes.

"We had to do mathematical calculations to find out how far the glass was regulating so they could look as far as possible , " Gislen said. And it shows that children need to be able to regulate much better than you think to be able to see underwater.

"Normally when you're in the water, everything is too blurry so the eyes can't find a way to regulate, it's not a normal reflex , " Gislen said. "But Moken children can do both at the same time - they can make the pupils smaller and change the shape of the lens . Seals and dolphins have similar abilities."

The adult Moken catches food mostly by launching javelins from above the water.

Gislen also did the same experiment with mature Moken people. They had no special sight under the water - perhaps this explains why the tribe's adults caught food largely from the javelin from the water. "As we age, the lens becomes less flexible, so it's easy to understand why they lost when the ability to regulate when underwater," Gislen said.

Gislen wondered if the Moken children had some unusual genes so they could see underwater or simply by practicing. To find out, she asked a group of European children to travel in Thailand, and a group of young Swedish children participated in a training course, in which they would dive into the water and watch the straight lines. in which direction. After 11 practice sessions in a month, both groups have the same underwater vision as the Moken children.

"Every child is different, but at some point their eyesight will suddenly improve ," Gislen said. "I asked if they did anything different and they said:" No, it's just that you look better now "".

The Moken's hometown was destroyed after a tsunami.

However, she also realized, European children will have red eyes, due to salt irritation, while Moken children have no problems . "Perhaps some adaptation has made them dive 30 times without being irritated , " she said.

Gislen recently returned to Thailand to visit the Moken tribe, but things have changed a lot. In 2004, a tsunami destroyed the Moken homeland. Since then, the Thai government has been very active in bringing them to the mainland, building inland areas and hiring tribal people to work in the National Park."This is very difficult , " Gislen said. " You want them to be safe and give them the best of modern culture, but it also makes them lose their own culture."

In an unpublished study, Gislen experimented on children who performed the first trial. Moken children, now about to be teenagers, can still see clearly underwater. She cannot test on many adults because they are too timid, but she is certain that they will lose their ability to look underwater when they get older."Adult eyes cannot regulate so much," she said.

Unfortunately, the children that Gislen experimented with were probably the last in the tribe to see underwater."They no longer spend a lot of time in the sea like before," she said, "so I doubt if there are any tribe children growing up in this era who will have that extraordinary visa."