By Drs. David Niesel and Norbert Herzog
Have you ever opened your eyes while diving in the ocean without a mask and realized that you really can't see very well? Well, the children among a nomadic sea faring people known as the Moken can see underwater with total clarity, but what is really interesting is that other children can acquire this ability too in just a matter of weeks.
The Moken people have historically been totally dependent upon the ocean surrounding the Mergui Archipelago, a group of 800 small islands off the southwestern coast of Myanmar. The Moken people are Austronesians who are thought to have migrated from southern China about 4000 years ago. For 8 to 9 months of the year, the Moken live aboard their boats, known as kabang, living on land in temporary camps only during the monsoon season. They live on what they can harvest from the sea and the beaches and by trading the sea life they gather with Chinese and Malay neighbors. There may be as few as 1000 Moken still living the traditional way.
Moken children spend much of their time in the water and participate in the gathering of seafood starting at an early age. As opposed to most of us, the Moken children see everything with perfect clarity when diving underwater. A Swedish scientist, Anna Gislen, has been studying the Moken for two decades to learn how this is possible. She measured how clear the underwater vision of 17 Moken children was and compared that with 18 European children all aged 7 to 13 years old. The Moken children had more than twice the visual acuity compared with European children.
Gislen hypothesized that part of the reason they can see more clearly under water is their ability to constrict their pupils. Just like with a camera lens, if you constrict the pupil, you increase the depth of field. That is the distance between the nearest and farthest objects that will be in focus. Measurements proved that Moken children constricted their pupils underwater to the maximum known limit for a human. However, there had to be more to this, somehow, either consciously or unconsciously, Moken children had to also be changing the shape of the lenses of their eyes to improve the focus of an object, called accommodating their lenses. This is exactly what she found. This ability is retained into adolescence. What is fascinating is that European children could be taught to make these same changes to their eyes to improve vision underwater. After 11 training sessions over one month, they developed the same visual acuity as Moken children. How long this took was different for each child, but their vision would suddenly improve. Interestingly, seals and dolphins have similar abilities to adapt their eyes.
The traditional Moken culture is rapidly disappearing as a result in part from a 2004 tsunami that destroyed much of the Moken homeland. Governments are relocating them further inland for their safety and providing other employment. Sadly, the life of these sea nomads, as they are also known, is changing and their children may not develop "dolphin eyes" because they will not be spending so much time diving. However, this is a remarkable example of how adaptable the human body can be.
Medical Discovery News is hosted by professors Norbert Herzog at Quinnipiac University, and David Niesel of the University of Texas Medical Branch. Learn more at www.medicaldiscoverynews.com.