Blue eyed see better in the dark

People with blue eyes may have better sight in dim conditions than those with brown eyes, according to LJMU research reported in New Scientist.

The theory could explain why the colour has persisted in certain populations, for example in Northern Europe where skies are darker.

The study, described as “preliminary,” by Dr Kyoko Yamaguchi is based on an idea she had when first moving to Europe, but the finding needs confirming in a larger study.

Kyoko, is based in the School of Environmental and Biological Sciences and specialises in studies the genetic basis of skin, hair and eye colour.

When she moved to Europe from Japan, she was struck by how much dimmer the lighting was in buildings, often finding it too dark to read by.

This made her wonder whether there was a biological basis for this weaker lighting, rather than just a cultural one. To learn more, she and her student Faith Erin Cain tested the vision of 40 people of European descent who had either blue or brown eyes.

After the volunteers sat in darkness for 30 seconds, the researchers gradually increased the brightness of the lighting until the participants were able to read a sequence of letters on a wall 3 metres away. Those with blue eyes needed a light level of 0.7 lux on average, compared with 0.82 lux for those with brown eyes.

According to a report in New Scientist, other experts say the idea that having blue eyes helps in dim conditions makes sense, but the number of volunteers in this study was too small to draw firm conclusions. “The concept is plausible,” says Cassie Ludwig at Stanford University in California. Pirro Hysi at King’s College London says: “This is possible, [but] not proven because the analyses were based on a small sample.”

If the finding is confirmed, it might help explain why blue eyes evolved in some populations in Northern Europe, says Dr Yamaguchi.

The current thinking is blue eyes were a side effect of selection for lighter skin and blonde hair, and the driving force behind this was a need to get sufficient vitamin D. Our bodies use ultraviolet rays to make vitamin D in the skin, so darker skin can result in vitamin D deficiency in regions with little sunlight.

However, blue eyes may be a disadvantage in bright light. Some studies suggest blue irises scatter more light than brown ones, degrading image quality.

Dr Yamaguchi hopes to secure funding for a larger study that would also include people with a wider range of eye colours, but Mackey says this may be a struggle. “Although eye colour is very interesting to the general public, it is really hard to get funding to do research in the area,” he says.