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Key points

• The macular pigments are carotenoids found within the retina, concentrated around the macula and anterior to the photoreceptors.
• There are three macular pigments. Lutein and zeaxanthin are wholly derived from the diet, while a third, meso-zeaxanthin, is produced in the retina from lutein.
• The macular pigments have a number of functions; they act as anti-oxidants and minimise free radical damage resulting from photo-oxidative damage, they absorb short wavelength visible (blue/violet) light which is potentially phototoxic, and they also appear to support dark adaptation and improve contrast sensitivity.
• Macular pigment levels differ between people, with an increased risk of age-related macular degeneration (AMD) in individuals with lower levels.
• Smoking causes a 400% increased risk of AMD, while low levels of macular pigments and anti-oxidants is associated with a 372% increased risk.
• Animal models suggest that reduced macular pigment levels increases the likelihood of developing AMD at a younger age.
• Macular pigment levels are influenced by genetic profile, and are reduced by smoking and obesity, short wavelength light cumulative exposure and the existing presence of drusen.
• Existing methods of macular pigment measurements include heterochromic flicker photometry, reflectometry, dual wavelength fundus autofluorescence and Raman spectroscopy.
• A new technique developed at Bristol University exploits the fact that the ability to see Haidinger’s brushes, an entoptic phenomenon relying on perception of polarised light, is related to the concentration of macular pigment.
• The ability of a patient to see Haidinger’s brushes (by correct identification of the rotation movement of the brushes) of increasingly difficult to see targets correlates well with macular pigment levels.
• A test takes, on average, 53 seconds to assess macular pigment levels and early trials suggest good reliability, repeatability and ease of use.
• Use of the technique, with an MPI unit, is hoped to allow screening for low levels and monitoring the impact of any intervention, such as lifestyle changes or dietary supplementation.