Dolphin Eyes: The Secret of Moken Children’s Underwater Vision

Children from the Moken tribe, a community of sea nomads living around the Surin Islands off the coast of Thailand, have demonstrated a unique ability to see clearly underwater without the aid of goggles. This phenomenon has drawn the attention of scientists since the late 1990s, who sought to understand how human eyes—normally adapted for land vision—could function in such a way underwater. ¹

The Moken people traditionally live a semi-nomadic lifestyle, traveling by boat and relying on the sea for food. Moken children often spend hours diving for clams, sea cucumbers, and other marine life. Unlike most humans, they are able to distinguish fine details underwater. ²

A research team led by Swedish scientists first studied this ability in 1999. They conducted underwater vision tests by placing patterned cards beneath the surface and asking Moken children to identify the designs. The children performed about twice as well as European children tested under the same conditions. ³

Human vision generally blurs underwater because light behaves differently than it does in air. Normally, the cornea bends light precisely to focus it on the retina. Underwater, however, the refractive power of the cornea decreases because water and the cornea have similar refractive indices. This causes the light to scatter rather than converge on a single point, producing a fuzzy image. ⁴

Recently, Maddie Massy, MPhil in Immunology, explained this unique human feature on her YouTube Channel.

She added, "The Moken children were able to change the shape of their eye lenses as well to better bend and focus the light. And they were able to do this so well, basically to the limits of human ability. And it wasn't clear to the researchers whether this was something that the Moken children were doing consciously or unconsciously."

The researchers initially hypothesized that Moken children might have myopia, a condition in which the focal point falls in front of the retina, potentially allowing clearer vision underwater. However, tests revealed that Moken children had normal land-based vision, ruling out myopia as an explanation. ⁵

Further studies suggested that two mechanisms were at work. First, Moken children could constrict their pupils underwater, reducing the amount of light entering the eye and improving sharpness, much like seals and dolphins. Second, they were able to alter the shape of their eye lenses to a degree close to the maximum possible for humans. This combination allowed them to compensate for the optical challenges of underwater vision. ³

Interestingly, these adaptations were observed only in children and not in adults. Scientists believe this may be due to age-related changes in the lens, which becomes less flexible over time, reducing the ability to adjust focus underwater. ¹

As the Moken lifestyle evolves and younger generations spend less time in the sea, researchers question whether this extraordinary ability will persist. The findings highlight how environmental demands can shape human physiology and reveal latent capacities in the human visual system that are rarely used in modern life. ²

The research on the Moken children has been published in Vision Research and continues to be cited in studies exploring the plasticity of human vision. ⁴

References

1. Carl Zimmer, “The Sea Nomad Children Who See Like Dolphins,” BBC Future, February 29, 2016. https://www.bbc.com/future/article/20160229-the-sea-nomad-children-who-see-like-dolphins.

2. Michelle Starr, “These Sea Nomad Children Can See Underwater Like Dolphins,” ScienceAlert, March 2, 2016. https://www.sciencealert.com/these-sea-nomad-children-can-see-underwater-like-dolphins.

3. Anna Gislén et al., “Superior Underwater Vision in a Human Population of Sea Gypsies,” Vision Research 46, no. 20 (2006): 3443–50. https://doi.org/10.1016/j.visres.2006.05.009.

4. UNILAD, “Moken Underwater Vision: Dolphin Eyes,” UNILAD, May 4, 2022. https://www.unilad.com/features/moken-underwater-vision-dolphin-eyes-thailand-tribe-perfect-20220504.

5. “The Children Who Can See Underwater,” Imperial Bioscience Review, October 9, 2020. https://imperialbiosciencereview.wordpress.com/2020/10/09/the-children-who-can-see-underwater/.

(Rh/Eth/MSM)