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

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Abstract

Visual function degrades with increasing age, in absence of frank disease, and affectsboth photopic and scotopic sensitivity. The mechanisms underlying these impairmentsmay be related to biological (e.g., neural, optical) and environmental (e.g., smoking,dietary) factors. Recent evidence suggests that visual function may be improved followingretinal carotenoid supplementation, both, in healthy and diseased eyes. Retinalcarotenoids accumulate within the retina to form the macular pigment (MP) - abiomarker of antioxidant status of the eye and retinal disease risk.The objectives of this thesis were manyfold. First, the extent of vision loss (particularlyscotopic sensitivity) in healthy ageing was examined. The results of this investigationshowed that dark adaptation recovery slows with increasing age despite no significantchange in visual acuity or fundus appearance. The technique described had excellentrepeatability and correlated well with previous research. The potential link betweenMP and dark adaptation was also examined. The results showed that macular pigmentoptical 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 onvisual function in a large group of observers aged between 50 and 90 years old. Thebaseline data from this clinical trial revealed very interesting findings with regards tounhealthy lifestyle behaviours, health status and statin use.Subjects taking statins were identified (n = 25) and matched with 25 participants notusing statins for age and body mass index. It was found that statin users had a higherproportion of males, higher prevalence of current smoking status and poorer generalhealth (e.g. hypertension, high cholesterol and heart disease). Statin users also hadsignificantly reduced MPOD, prolonged photostress recovery time, and deficits in anumber 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, higherprevalence of high cholesterol and lower fruit and vegetable intake. MPOD was alsoreduced 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, placebocontrolledstudy. Active formulation consisted of 20 mg lutein combined with vitaminsand minerals. Data were collected at baseline, 6 months and 12 months. The resultsshowed that, despite a 24% MPOD increase in the active group, there were no significantdifferences between the two groups over the three visits for any of the visualparameters.Given the increasing size of the older adult population in developed countries, researchaimed at slowing or reversing age-related declines in vision is much needed both froman economical and psycho-social perspective. The results of the studies presented inthis thesis show that lifestyle, health status and certain medications can adversely affectvisual function in normal ageing. MP augmentation, however, had no effect on visualfunction. Further research is warranted, particularly paying close attention to subjectsengaging in several unhealthy lifestyle/dietary behaviours, statin users and those withlow MPOD and suboptimal visual function.

Keyword(s)

Macular pigment; Retinal ageing; Visual function

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