15,15'-cis-β,β-Carotene is a very powerful antioxidant and a precursor to Vitamin A which is an essential nutrient, required by the retina of the eye in the form of a specific metabolite, the light-absorbing molecule retinal, that is necessary for both low-light (scotopic vision) and color vision. As a part of the carotenoid family of compounds it is a very effective scavenger and quencher of singlet oxygen and free radicals. Prooxidant.