Macular pigment and its contribution to visual performance in the older human eye

Visual function degrades with increasing age, in absence of frank disease, and affects both photopic and scotopic sensitivity. The mechanisms underlying these impairments may be related to biological (e.g., neural, optical) and environmental (e.g., smoking, dietary) factors. Recent evidence suggests that visual function may be improved following retinal carotenoid supplementation, both, in healthy and diseased eyes. Retinal carotenoids accumulate within the retina to form the macular pigment (MP) a biomarker of antioxidant status of the eye and retinal disease risk. The objectives of this thesis were manyfold. First, the extent of vision loss (particularly scotopic sensitivity) in healthy ageing was examined. The results of this investigation showed that dark adaptation recovery slows with increasing age despite no significant change in visual acuity or fundus appearance. The technique described had excellent repeatability and correlated well with previous research. The potential link between MP and dark adaptation was also examined. The results showed that macular pigment optical density (MPOD) was correlated with a specific parameter of dark adaptation (S2) a sensitive marker of functional degradation in normal ageing and retinal disease. The main part of this thesis sought to investigate the effect of MP augmentation on visual function in a large group of observers aged between 50 and 90 years old. The baseline data from this clinical trial revealed very interesting findings with regards to unhealthy lifestyle behaviours, health status and statin use. Subjects taking statins were identified (n = 25) and matched with 25 participants not using statins for age and body mass index. It was found that statin users had a higher proportion of males, higher prevalence of current smoking status and poorer general health (e.g. hypertension, high cholesterol and heart disease). Statin users also had significantly reduced MPOD, prolonged photostress recovery time, and deficits in a number of dark adaptation parameters. In a separate analysis of the whole group (n = 74, mean age 65.51), smokers were found to have reduced MPOD, slower S2, higher prevalence of high cholesterol and lower fruit and vegetable intake. MPOD was also reduced among obese subjects. The impact of MP augmentation on visual function in normal older subjects was assessed (n = 74, mean age 65.51) in a 12 month, randomized, double-blind, placebocontrolled study. Active formulation consisted of 20 mg lutein combined with vitamins and minerals. Data were collected at baseline, 6 months and 12 months. The results showed that, despite a 24% MPOD increase in the active group, there were no significant differences between the two groups over the three visits for any of the visual parameters. Given the increasing size of the older adult population in developed countries, research aimed at slowing or reversing age-related declines in vision is much needed both from an economical and psycho-social perspective. The results of the studies presented in this thesis show that lifestyle, health status and certain medications can adversely affect visual function in normal ageing. MP augmentation, however, had no effect on visual function. Further research is warranted, particularly paying close attention to subjects engaging in several unhealthy lifestyle/dietary behaviours, statin users and those with low MPOD and suboptimal visual function.