Biomarkers are being sought with the aims of early identification of those at cognitive risk and identification of possible pathways that could be targeted for preventive intervention. The eye is often regarded as a window to the brain, and is relatively easy to observe noninvasively. Many pathologic changes in the eye are thought to reflect those throughout the central nervous system.
Macular pigment in the eye is comprised of the carotenoids lutein, zeaxanthin, and meso-zeaxanthin, which selectively accumulate in the central retina and are neuroprotective. Lutein and zeaxanthin are entirely of dietary origin, whereas meso-zeaxanthin is thought to derive at least in part from retinal lutein through a poorly understood bioconversion process. These carotenoids are also present in the brain, and evidence suggests a close correlation between retinal and brain concentrations. The authors of this study investigated the relationship between macular pigments and cognitive function in 4453 adults aged 50 years or older as part of The Irish Longitudinal Study on Aging. Macular pigment optical density was determined using customized heterochromatic flicker photometry, a quick and noninvasive way of measuring pigment concentrations. The results showed that lower macular pigment optical density was associated with poorer performance on the mini-mental state examination and on the Montreal cognitive assessment. Individuals with lower macular pigment optical density also had poorer prospective memory, took longer time to complete a trail-making task, and had slower and more variable reaction times on a choice reaction time task. There was no significant association with verbal fluency, word recall, visual reasoning, or picture memory. The authors suggest that xanthophyll carotenoids may impact cognitive function, and underscored the need for exploration of novel, noninvasive biomarkers for cognitive vulnerability and preventive strategies.
Feeney J, Finucane C, Savva GM, Cronin H, Beatty S, Nolan JM, Kenny RA: Low macular pigment optical density is associated with lower cognitive performance in a large, population-based sample of older adults. Neurobiology of Aging 34 (11): 2449-2456 (2013).
