Superior Underwater Vision Shows Unexpected Adaptability of the Human Eye
Anna Gislen & Erika Schagatay 2011
doi 10.2174/978160805244811101010164
Adaptability of the eye is a key feature in a semi-aquatic mammal:
several optical & physiological strategies can be used to allow functioning of the eye in the 2 media: air & water.
Human eyes are considered to be adapted to vision in air:
2/3 of the refractive power is derived from the curved cornea,
this effect is lost under water.
... children of Sea Nomad groups in SE.Asia appeared to have much better underwater vision than expected,
this allowed efficient collection of small shells from a non-contrasting background, without visual aids.
Studies on the visual acuity of such groups were carried out:
how was the observed adaptability of the eye achieved?
Standardized optical methods were
- adopted to field conditions,
- used to reveal how the Sea Nomad children see under water.
Results showed
- a high adaptability of the human eye to the underwater environment,
- the visual acuity of the Sea Nomad children was twice that of a European control group,
- training in non-diving children evoked the same adaptive responses as in Sea Nomads.
The mechanisms responsible for this superior underwater vision were
- heavy accommodation &
- concurrent pupil constriction,
these features were previously observed in semi-aquatic mammals & birds.
This may be an interesting example of convergent evolution.
The human eye proved to be flexible & adaptable enough to function underwater, with an uncompromised function in air.
An explanation for this surprising adaptation in a terrestrial mammal could be: it has evolved during a phase with selective pressure for foraging under water.
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