Photo by: Vegas ER
Here’s a question suited for these hot summer months. It’s one your kids may have asked you after they emerged from the ocean or a pool, or perhaps it’s one you’ve wondered about yourself: How come I can’t see well underwater without goggles or a mask?
Even when conditions are crystal clear, such as in pool or at an unspoiled Caribbean lagoon, we humans need help to see well underwater. Sure, we can make out objects (that sunken pool toy on the bottom, for example), but focusing is just impossible (not to mention painful, given how chlorine or salt water feels on our open eyes).
Why is that?
The answer is related to the structure of the eye and how it focuses light.
On its way to the retina, light passes through two lenses: the cornea, on the outside of the eye, and another lens inside the eye. Most of the refraction – or bending – of light rays, which is the key to focusing, occurs when light passes through air into the cornea, which is much denser than the atmosphere. (Think of a spoon in a glass a water – the spoon looks like it’s bending, but what we are seeing is an illusion caused by the bending of the light rays as they pass between the air and water).
The cornea accounts for about two-thirds of the eye’s refractive power, but because water and our corneas have similar densities, not much bending occurs when light passes between them. And our interior lens is not powerful enough to accommodate for the refraction that is not occurring in the cornea, which results in unfocused light rays hitting our retinas.
The bottom line is that our eyes have evolved to accommodate our vision on land, not in water. Fish, on the other hand, not surprisingly have developed eyes that specifically accommodate their aquatic environment.
If you’d like to learn more about the mechanics of seeing underwater, you might want check out these informative online sources here and here.
