Retinal undergoes an irreversible change in shape when it absorbs light ; this change causes an alteration in the shape of the protein which surrounds the retinal .
That alteration then induces the physiological process which results in vision .
Retinal undergoes an irreversible change in shape when it absorbs light ; this change causes an alteration in the shape of the protein which surrounds the retinal , and that alteration then induces the physiological process which results in vision .