Hammond, C.J., Liew, S.H., Van Kuijk, F.J., Beatty, S., Nolan, J.M., Spector, T.D. and Gilbert, C.E. (2012) The Heritability of Macular Response to Supplemental Lutein and Zeaxanthin: A Classic Twin Study. Investigative Ophthalmology & Visual Science, 53, 4963-4968.