Supplementation with lutein increases macular pigment optical density by 27%; which is correlated with benefits in visual function.
Gunther, Weigert, Semira Kaya, Berthold Pemp, Stefan Sacu, Michael Lasta, Rene Marcel Werkmeister, Nikolaus Dragostinoff, Christian Simader, Gerhard Garhofer, Ursula Schmidt-Erfurth, and Leopold Shcmetterer. Effects of Lutein Supplementation on Macular Pigment Optical Density and Visual Acuity in Patients with Age-Related Macular Degeneration. Invest Ophthalmol Vis Sci. October 2011; 52(11): 8174-8. http://www.iovs.org/content/52/11/8174.abstract