Macular pigment measurement
Objective technique provides valuable tool in macular health assessment
John M. Nolan PhD
Macular pigment optical volume (MPOV) measurements obtained with the dual-wavelength autofluorescence technique can provide a standardised means of assessing the nutritional health of the macula and the brain, according to a study conducted by Prof John M. Nolan PhD and his associates at the Nutrition Research Centre Ireland, School of Health Science, Waterford Institute of Technology, Waterford, Ireland.
“This research is another step in the validation of this highly repeatable image-based technique to measure the full amount of macular pigment in the living person and this should represent a new standard,” Prof Nolan told EuroTimes in an interview.
He noted that a standardised method of measuring and recording macular pigment levels will allow clearer interpretation of the impact of higher and lower concentrations of the pigments on visual quality. It should also eventually allow the establishment of a normative database so that treatment effects can be closely monitored in both a research and clinical setting.
The study, published in the December 2019 issue of the Journal Translational Vision Science & Technology, involved 393 participants who ranged in age from 21 to 88 years, with a mean age of 55.5 years. None of those included had a critical medical condition or a previous history of oral carotenoid supplementation. However, 37% had a medical diagnosis of AMD or a neurocognitive disorder.
All participants underwent examination with the Heidelberg Engineering SPECTRALIS with the investigational Macular Pigment Optical Volume (MPOV) Module to measure macular pigment optical volume (MPOV) and macular pigment optical density (MPOD) at four foveal eccentricities (0.23°, 0.51°, 0.98°, 1.76° [7° as reference point]). The researchers also evaluated serum concentrations and dietary intake of the macular pigments lutein and zeaxanthin.
The investigation showed that the participants’ mean MPOV was 5,094 and ranged from 527 to 10,652. MPOV was inversely correlated with body mass index (p=0.002) and positively correlated with education (p=0.014) and serum concentrations of lutein and zeaxanthin (p<0.001 and p<0.001, respectively). However there were no significant correlations between MPOV and the clinical and demographic variables, including medical diagnosis, dietary intake, smoking status and sex.
The SPECTRALIS MPOV Module uses confocal scanning laser ophthalmoscopy with blue (486nm) and green (518nm) laser diodes for auto fluorescent excitation. Because macular pigment is yellow, it absorbs blue light four times more strongly than it absorbs green light. Therefore, where macular pigment is present the blue light-excited autofluorescence will be lower than that of green light-excited AF at the same location. The MPOV value is a measure of MP density as well as its distribution within the macula, providing a measurement of the total MP across all eccentricities.
Prof Nolan noted macular pigments act as a blue filter, protecting the photoreceptors from harmful blue rays, reducing chromatic aberration and scattered blue light, in turn reducing glare and enhancing contrast sensitivity. Macular pigments also have antioxidant and anti-inflammatory properties.
Macular pigments also tend to be lower in patients with age-related macular degeneration. Furthermore, in the AREDS2 trial and other studies, formulas containing lutein and zeaxanthin were 10% more effective in slowing the progression of intermediate dry AMD as the original betacarotene formulation, he said.
In addition, post-mortem studies have shown that the amount of macular pigment in the macula is highly correlated with the amount of macular pigment in the brain. Research has also shown that people with higher concentrations of the carotenoids in their macula had better cognitive abilities, whereas those with Alzheimer’s disease tended to have highly deficient concentrations.
Some studies have documented improvements in quality of life in patients with cognitive disorders who received carotenoid supplementation. A major study is now under way to determine the validity of these promising findings.
“If you expect that having an antiinflammatory agent with antioxidant propertiesis good for brain health then one could see macular pigment levels as a biomarker for brain nutrition,” Prof Nolan added.
John Nolan: email@example.com