THAT'S THE WHY:When actor Patrick Duffy donned those alarming yellow swimming trunks and dived into the leading role in The Man from Atlantisin the 1970s TV series, his character was equipped with a few physical attributes that made him nifty in the water.
His webbed fingers and toes were built for swimming at speed, and he had a pair of lungs that didn’t require annoyingly frequent air changes and eyes that were highly sensitive to light.
But there’s another, less blindingly obvious feature that his amphibious character’s eyes must have had: the ability to focus well underwater – which is something we land-loving humans lack.
Why do we find it so hard to see clearly underwater? Quite apart from the discomfort many of us feel trying to open our unshielded peepers there in the first place, things appear blurry when we are immersed because of the refractive index of water and the fact that we can’t curve our corneas enough to compensate.
Or as LJF Hermans put it in Europhysics Newsin 2006: "The reason is obvious: since the index of refraction of the inner eye is practically that of water, we miss the refractive power of the strongly curved cornea surface."
One way around it is to get some air in front of the eyes. “We really need to restore the air-water interface in front of the cornea, and that is precisely what our diving mask does,” he adds.
Of course goggles perform a similar function, if you don’t want to look overdressed at the local pool.
– CLAIRE O’CONNELL
