Underwater Vision – Evolution or Adaptation

It is officially summer, which means making the absolute most out of three months of sunshine and swimming! While you may choose to lounge poolside on those hot sunny days, with so many idyllic lakes and ponds, why limit yourself to concrete and chlorine…

Regardless of where you’re taking a dip, you’ll like to close your eyes underwater or else only open them for brief moments of blurry reflection on where you’re headed. For one thing, everything is blurry underwater so what is there to see? And for another thing, if you’re swimming in a pool your eyes will probably sting if they’re open for any length of time.

Humans are not particularly well adapted to seeing underwater. Ever wonder why?

“To see clearly above land, you need to be able to refract light that enters the eye onto the retina. The retina sits at the back of the eye and contains specialized cells, which convert the light signals into electrical signals that the brain interprets as images.

Light is refracted when it enters the human eye because the outer cornea contains water, which makes it slightly denser than the air outside the eye. An internal lens refracts the light even further.

When the eye is immersed in water, which has about the same density as the cornea, we lose the refractive power of the cornea, which is why the image becomes severely blurred.”¹

Evolution or Adaptation?

So, people just can’t see well underwater, and we should all just deal with that, right? We have goggles of every shape and style, even prescription goggles if we want to have our best vision possible underwater, so what else is there to know?

What if were possible that people could in fact adapt to seeing underwater more like seals or dolphins?

“Normally when you go underwater, everything is so blurry that the eye doesn’t even try to accommodate, it’s not a normal reflex,” says Gislen. “But the Moken children [of Thailand] are able to do both – they can make their pupils smaller and change their lens shape. Seals and dolphins have a similar adaptation.”²

As it turns out, “Unlike most people, the children of a Thailand tribe see with total clarity beneath the waves.”³

The entire story of the Moken children and their incredible underwater visual acuity written by Helen Thomson for the BBC shares the work of Anna Gislen, a research scholar at the University of Lund, Sweden, and her time with the Moken children.

The fascinating discovery of real-time visual adaption highlights our ability as humans to physically adapt to conditions we otherwise might not believe we could acclimate to. In fact, Gislen found that European children can be intentionally trained to constrict their pupils when diving and enhance their underwater visual acuity much like the Moken children have done automatically. Thus, it’s possible underwater vision can be learned over time, you don’t simply have to grow up on the coast of Thailand to see that.