Macular Pigment and its Contribution to Spatial Vision
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3. MEDICAL AND HEALTH SCIENCES
Purpose:The optical properties and anatomic distribution of macular pigment (MP) are such that it may theoretically contribute to visual performance by attenuating the effects of chromatic aberration and light scatter. The Collaborative Optical Macular Pigment Assessment (COMPASS) study is a placebo-controlled, randomized and double-blind clinical trial designed to assess whether MP optical density (MPOD) influences spatial vision by attenuating short wavelength light. Preliminary analysis of baseline findings, prior to supplementation, is presented here. Methods:119 young (mean=29+/-6 years) healthy subjects were recruited. The spatial profile of MPOD was assessed by customized heterochromatic flicker photometry. Visual performance was assessed by psychophysical tests including recognition acuity (VA), mesopic contrast sensitivity and photopic contrast sensitivity across spatial frequencies ranging from 1.0 cycles per degree (cpd) to 20.7cpd. Subjects also completed a visual function questionnaire designed to generate a quantitative index of subjects perceived functional performance. Results:Mean peak MPOD was 0.50+/-0.19. Pearson’s correlation coefficient showed a statistically significant positive relationship between best corrected high contrast VA and MPOD at 0.25, 0.50, 1.0, 1.75, 3.0 degrees of retinal eccentricity and with overall MPOD (r=0.202, p=0.029; r=0.211, p=0.022; r=0.190, p=0.039; r=0.320, p=0.000; r=0.233, p=0.011; r=0.243, p=0.008 respectively). Low contrast VA correlated with central MPOD at 0.25 degrees but at no other retinal eccentricity (r=0.186, p=0.044). The questionnaire derived visual performance index revealed no significant correlation with baseline MPOD. Photopic contrast thresholds exhibited an inverse and statistically significant correlation with MPOD at 0.25, 0.50 and 1.75 degrees of retinal eccentricity but only for the lowest spatial frequency of 1.0 cpd (r=-0.239, p=0.009; r=-0.200, p=0.030; r=-0.230, p=0.012 respectively). Mesopic contrast thresholds showed no statistical correlation with baseline MPOD. Conclusions:Our results illustrate the difficulties inherent in assessment of MPOD and visual performance using cross sectional, observational methodology. Measures of central visual function including visual acuity and contrast sensitivity reveal variable associations with baseline MPOD. The outcome of this longitudinal, placebo-controlled and randomized supplementation trial will serve to more fully elucidate the potential for visual performance enhancement through MPOD augmentation.
Akkali, M., Nolan, J., Beatty, S., Davison, P. O'Dwyer, V., Scanlon, G., Loughman, J.: Macular Pigment and Its Contribution to Spatial Vision. Association for Research in Vision and Ophthalmology Conference Investigative Ophthalmology and Visual Science. 2009.
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