Macular pigment and contrast sensitivity in healthy adults

Introduction: Some past data has shown that macular pigment (MP) is related to improved contrast sensitivity (CS) under certain conditions. The mechanism for this improvement, however, is unclear. The question of whether higher MP improves CS under carefully controlled optical conditions (e.g., similar to refractive correction) is not known. Methods: 22 participants (M=28.45 +/-10.36 years; 68% female; BCVA 20:30 or better) provided photopic contrast sensitivity functions (from measurements at 1.6, 3.2, 8, 16, and 24 cpd, with spatial frequency presentation randomized) using a simple optical device. The optical system used 520 nm lasers (not absorbed by MP) that were made Lambertian using two integrating spheres with a 3.5-deg circular exit port. These beams were combined with a beam splitter that allowed constant measurement of light output and contrast modulation using sine-wave gratings on glass. MP optical density (OD) was measured using customized heterochromatic flicker photometery (peak 460 nm, 1-degree test stimulus). Results: MPOD was not significantly related to CS at any measured frequency (range in correlation p-values, 0.92-0.41). Conclusions: The general finding that MP increases CS under glare conditions is reasonable: by reducing a veiling glare source (with significant SW energy), the visibility of a target would be increased. A pure filtering mechanism makes less sense in the absence of a glare source. If MP reduces the luminance of a grating target, CS would also be expected to be reduced (CS is positively related to luminance). The results of this study suggest that, under carefully controlled optical conditions, MP is not related to CSF in young healthy subjects. Interventions that have found a relation, therefore, are likely achieving this change through some other mechanism, either direct and physiological or through some health benefit (e.g., reduced oxidative/inflammatory stress).