Complex sentence: 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.
Split into simpler sentences: Retinal undergoes an irreversible change in shape when it absorbs light. This change of shape causes a change in the shape of the protein which surrounds the retinal, and that change induces the physiological process which results in vision.