Did you know your eyes have natural night vision mode?

Eyes have an in-built night vision mode, say scientists who found that retina changes its light-sensing cells to see under moonlight and starlight. Earlier, retinal circuits were thought to be unchanging and programmed for specific tasks. However, scientists have now identified how the retina reprograms itself for different light scenarios.

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“To see under starlight, biology has had to reach the limit of seeing an elementary particle from the universe, a single photon,” said Greg Field, an assistant professor at Duke University in the US. The findings, published in the journal Neuron, show that the reprogramming happens in retinal cells that are sensitive to motion. Even in the best lighting, identifying the presence and direction of a moving object is key to survival for most animals.

Detecting motion with a single point of reference does not work very well. Vertebrates have four kinds of motion-sensitive cell retinas, each responsive to a motion that is up, down, right or left. In humans, four per cent of cells account for directional neurons to send signals from the retina to brain.

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In a study with mouse retinas conducted under a microscope in a dark room equipped with night vision eye pieces, researchers found that the retinal cells sensitive to upward movement change their behaviour in low light. The ‘up’ neurons will fire upon detecting any kind of movement, not just upward.

In low light conditions, a weak signal of motion from the ‘up’ neurons, coupled with a weak signal from any of the other directional cells can help the brain sense movement. The loss of motion perception is a common complaint in human patients with severe vision loss.