A growing interest in macular pigment has highlighted the need for further investigation into environmental and genetic factors which may influence individual density and whether these levels can be increased. This thesis has aimed to address these fundamental questions through a systematic review of the current literature, a cross-sectional analysis of environmental and genetic factors associated with macular pigment and a randomised, placebo-controlled trial using a lutein and zeaxanthin supplement. Environmental and genetic factors affecting individual ability to respond were also investigated. Integral to macular pigment research is the ability to accurately measure macular pigment in vivo. This thesis also aimed to assess repeatability of the widely used HFP method, and to compare this technique to fundus reflectometry using the Viscucam 200. A statistically significant increase in serum lutein and macular pigment in response to supplementation was demonstrated by both the systematic review and randomised, placebo-controlled trial within this thesis. Both studies also show great variability in the response of macular pigment. When associations with macular pigment and serum carotenoid concentrations were examined cross-sectionally, established relationships were replicated with regards to baseline and environmental determinants of serum lutein and macular pigment. PTe taster status was not significantly associated with dietary intake of lutein and zeaxanthin. With regards to measurement of macular pigment, measures taken by the. Visucam 200 were found to be repeatable but not comparable to HFP using the MPS 1000. This thesis demonstrated good repeatability of the MPS 1000 over both short and longer-term periods making it useful for cross-sectional and longitudinal studies . To conclude, environmental and genetic factors found to be significantly associated with baseline macular pigment in previous studies have been replicated in the current study and new association identified, including environmental and genetic factors associated with macular response. Newly identified associations warrant further investigation.