There’s more than what meets the eye

There is a saying that your eyes are the windows to your soul.

Quite literally, you can tell a lot about a person’s emotional state from their eyes. This is reflected in the pupil – the opening to the eye, which dilates or contracts to regulate the amount of light coming into the eye.

Melanopsin, a blue-light sensitive protein in the eye establishes the rhythm of the day-night cycle and the familiar constriction of the pupil to bright light.

They then measured brain activity with a functional MRI and found that the visual pathway of the brain responded to the stimulation caused by melanopsin.

This photopigment also supports reflexive visual function in people – automatic visual reflexes that occur even when the person is not aware.

But what effect melanopsin has on conscious visual perception is less known and to find out more about this, researchers from the Perelman School of Medicine and School of Arts and Sciences at the University of Pennsylvania created a special pulse of light that stimulates only the melanopsin cells of the eye but is invisible to the cones.

This light was created using a machine that can switch back and forth between computer-designed “rainbow” light.

The researchers then had four people watch this light pulse while their pupil response was recoded. The scientists confirmed that the light pulse evokes a slow and reflexive constriction of the pupil which is characteristic of melanopsin stimulation.

They then measured brain activity with a functional MRI and found that the visual pathway of the brain responded to the stimulation caused by melanopsin.

This shows that people have a conscious visual experience of the stimulation caused by melanopsin.

20 additional participants observed melanopsin light pulses and were asked to rate different perceptual qualities. They reported the melanopsin light stimulation as blurry kind of brightness, quickly fading and as an unpleasant experience.

This study provides insight into excessive light sensitivity experienced by some people (photophobia) who are often in pain as a result.

There’s more than what meets the eye. Our eyes help us see our world around us, but studies show us that they also have other important biological functions such as automatic visual reflexes which produce a conscious reaction in our brain.

Source: Proceedings of the National Academy of Sciences