LONDON - Seemingly dead cells manipulate the lens of a fish eye to help them see colours by day and navigate by night, according to a new study.

It was previously known that the lens of the eye largely consists of lifeless cells. Now Lund University researchers in Sweden have discovered another fascinating facet of the eye lens.

For instance, lens in blue acara, a common aquarium fish, activates some of its lifeless cells every morning and evening to change the concentration of protein in the cell fluid. The change is hardly measurable, but its effect is of major importance.

‘With this strategy, the fish get better colour vision during the day and can see better in the dark at night,’ said Marcus Schartau, doctoral candidate in Ronald Kroger’s research team at the Department of Cell and Organism Biology at Lund.

It is the amount of protein in the lifeless cells that makes the light refract in the right way. What happens in the morning in the blue acara eye is that the lens adapts the protein concentration so that the lens can focus light of various wave lengths (colours) at one and the same point.

The fish can then see sharp colour images. This is called making the lens multifocal.

In the evening the protein concentration is restored to the same level as before the morning change. The lens can then only focus a single wavelength on the retina. The eye thereby loses its ability to create sharp colour images, but instead utilises the wavelengths that are most important for night vision. This is referred to as making the lens monofocal.

This strategy, switching between the two lens types every day, is something humans lack. Our monofocal lens is simpler in construction, but thanks to our greater depth of focus, we can still see different colours in daylight, said a Lund release.