How vision begins

Researchers at the Paul Scherrer Institute PSI have deciphered the molecular processes that first occur in the eye when light hits the retina. The processes – which take only a fraction of a trillionth of a second – are essential for human sight. The study has now been published in the scientific journal Nature.

It only involves a microscopic change of a protein in our retina, and this change occurs within an incredibly small time frame: it is the very first step in our light perception and ability to see. It is also the only light-dependent step. PSI researchers have established exactly what happens after the first trillionth of a second in the process of visual perception, with the help of the SwissFEL X-ray free-electron laser of the PSI.

At the heart of the action is our light receptor, the protein rhodopsin. In the human eye it is produced by sensory cells, the rod cells, which specialise in the perception of light. Fixed in the middle of the rhodopsin is a small kinked molecule: retinal, a derivative of vitamin A. When light hits the protein, retinal absorbs part of the energy. With lightning speed, it then changes its three-dimensional form so the switch in the eye is changed from “off” to “on”. This triggers a cascade of reactions whose overall effect is the perception of a flash of light.

Read more on the PSI website

Image: PSI researcher Valérie Panneels purifies the red protein rhodopsin in order to examine it later at the SwissFEL X-ray free-electron laser

Credit:  Scanderbeg Sauer Photography