Superior Underwater Vision in a Sea Gypsies

Anna Gislén, Marie Dacke, Ronald HH Kröger, Maths Abrahamsson, Dan-Eric
Nilsson & Eric J Warrant 2003
"Superior Underwater Vision in a Human Population of Sea Gypsies"
Curr.Biol.13:833-6

Humans are poorly adapted for underwater vision. In air, the curved corneal
surface accounts for 2/3 of the eye's refractive power, and this is lost
when air is replaced by water. Despite this, some tribes of sea gypsies in
SE.Asia live off the sea, and the children collect food from the sea floor
without the use of visual aids [2]. This is a remarkable feat when one
considers that the human eye is not focused underwater and small objects
should remain unresolved. We have measured the visual acuity of children in
a sea gypsy population, the Moken, and found that the children see much
better underwater than one might expect. Their underwater acuity (6.06
cycles/degree) is more than twice as good as that of European children (2.95
cycles/degree). Our investigations show that the Moken children achieve
their superior underwater vision by maximally constricting the pupil (1.96
mm compared to 2.50 mm in Eur.children) and by accommodating to the known
limit of human performance (15-16 D) [3]. This extreme reaction-which is
routine in Moken children-is completely absent in European children. Because
they are completely dependent on the sea, the Moken are very likely to
derive great benefit from this strategy.

(If someone is interested in reading the whole paper, I can send the pdf.)