Lutein and zeaxanthin are carotenoids (secondary plant substances). Both compounds occur naturally in the retina, particularly the macula lutea, and in the lens of the human eye. The macula lutea (yellow spot) is responsible for central vision and the area of the retina with the highest density of visual cells. Like all Pure Encapsulations products, lutein/zeaxanthin is also manufactured according to strict international standards. To ensure high product quality over time, the entire process, from production to storage, is constantly monitored. Internal and external quality controls are implemented at every stage.