Macular Pigment and its Contribution to Visual Performance and Experience

Chaitanya Akkali, Mukunda (2011) Macular Pigment and its Contribution to Visual Performance and Experience. Masters thesis, Waterford Institute of Technology.

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Abstract

Introduction The carotenoids lutein (L), zeaxanthin (Z) and meso-Z (MZ) accumulate at the macula where they are collectively referred to as macular pigment (MP). Scientific research continues to explore the function(s) of MP in the human retina, with two main hypotheses premised on its putative capacity to (1) protect the retina from (photo)-oxidative damage by means of its optical filtration and/or antioxidant properties, the so-called protective hypothesis and (2) influence the quality of visual performance by means of selective short wavelength light absorption prior to photoreceptor light capture, thereby attenuating the effects of chromatic aberration and light scatter, the so-called acuity, visibility and glare hypotheses. The current epidemic of age-related macular degeneration (AMD) has directed researchers to investigate the protective hypothesis of MP, while there has been a conspicuous lack of work designed to investigate the role of MP in visual performance Objectives This M.Sc. (by Research) thesis has four primary objectives: 1. To present and critically appraise the current literature germane to the contribution of MP, if any, to visual performance and experience 2. To assess whether MP optical density (MPOD) is associated with visual performance (Study One) 3. To investigate whether augmentation of MPOD enhances visual performance in normal subjects (Study Two) 4. To assess whether MPOD is associated with colour discrimination and matching (Study Three) Methods Study One: The Relationship between Macular Pigment and Visual Performance One hundred and forty-two young healthy subjects were recruited. MPOD was assessed by customised heterochromatic flicker photometry (cHFP). Visual performance was assessed by psychophysical tests including best corrected visual acuity (BCVA), mesopic and photopic contrast sensitivity, glare disability, photostress recovery time (PRT). Study Two: The Impact of Macular Pigment Augmentation on Visual Performance in Normal Subjects One hundred and twenty-one normal subjects were recruited. The active (A) group consumed 12mg of L and 1mg of Z daily. MPOD was assessed by cHFP. Visual performance was assessed as BCVA, mesopic and photopic contrast sensitivity, glare disability, photostress, and subjective visual function. Subjects were assessed at baseline; three; six; twelve months (V1, V2, V3 and V4, respectively). Study Three: Macular Pigment: its Associations with Colour Discrimination and Matching One hundred and two normal subjects were recruited. Colour vision was assessed with the Farnsworth-Munsell 100 Hue test (FM100), Moreland match on the Heidelberg Multi Colour (HMC) Anomaloscope, and a customised short wavelength automated perimetry (cSWAP) technique at the foveola and at 1°, 2°, 3°, 4° and 5° of retinal eccentricity. MPOD spatial profile was measured using cHFP. Results Study One: The Relationship between Macular Pigment and Visual Performance We report a positive and statistically significant relationship between BCVA and MPOD across its full spatial profile (r = 0.237 to 0.308, P < 0.01). MPOD was also positively and significantly related to both mesopic and photopic contrast sensitivity (at 7.5 cycles per degree (cpd) and 11.8 cpd), but was confined to the central MPOD at 0.25° and 0.50° of retinal eccentricity (r = 0.167 to 0.220, P < 0.05, for all). Glare disability and PRT were unrelated to MPOD spatial profile (P > 0.05). Study Two: The Impact of Macular Pigment Augmentation on Visual Performance in Normal Subjects Central MPOD increased significantly in the A group (P < 0.05) but not in the placebo (P) group (P > 0.05). This statistically significant increase in MPOD in the A group was not, in general, associated with a corresponding improvement in visual performance (P > 0.05, for all variables), with the exception of a statistically significant time/treatment effect in “daily tasks comparative analysis” (P = 0.03). At V4, we report statistically significant differences in mesopic contrast sensitivity at 20.7 cpd, mesopic contrast sensitivity at 1.5 cpd under high glare conditions, and light/dark adaptation comparative analysis between the lower and the upper MP tertile groups (P < 0.05). Study Three: Macular Pigment: its Associations with Colour Discrimination and Matching Total error scores (TES) and % partial error scores (%PES) on the FM100 were uncorrelated to MPOD. Moreland matches shown a significant long wavelength shift with MPOD at between 1° and 3° (at 1.75°, r = 0.489, P <0.001). Sensitivities on cSWAP using foveal targets were significantly inversely correlated with MPOD at both 1.75° (r = -0.461, P < 0.001) and 3° (r = -0.393, P < 0.001). Partial correlation analysis suggests that none of these findings can be attributed to age effects within the range 18 to 40 years. Conclusions Study One: The Relationship between Macular Pigment and Visual Performance Measures of central visual function, including BCVA and contrast sensitivity, were positively associated with MPOD. Glare disability and photostress recovery were unrelated to MPOD Study Two: The Impact of Macular Pigment Augmentation on Visual Performance in Normal Subjects We report that a significant increase in central MP following L supplementation does not, in general, impact on visual performance in young normal subjects, and our pre-specified hypothesis that MP augmentation would result in improved visual performance and/or comfort by 12 months, in those randomised to the A arm, remains unproven. However, subjects with high MP following L supplementation demonstrate visual benefits with respect to glare disability and mesopic contrast sensitivity. Further study into MP and its relationship with visual performance is warranted to enhance our understanding of this pigment‟s role. However, in order to investigate the impact of MP augmentation on visual performance, the findings of our study suggest that we should direct our attention to, a) subjects with low baseline central MP levels, b) subjects with suboptimal visual performance and c) subjects with symptoms of glare disability Study Three: Macular Pigment: its Associations with Colour Discrimination and Matching Our findings suggest that dietary supplementation to increase MPOD is unlikely to adversely affect hue discrimination. The association of MPOD with cSWAP may be a temporally limited effect to which the visual system normally adapts. We suggest that cSWAP may provide a clinical tool for assessing short-wavelength foveal sensitivity

Item Type: Thesis (Masters)
Uncontrolled Keywords: Macular pigment
Departments or Groups: Macular Pigment Research Group
Divisions: School of Science > Department of Chemical and Life Sciences
Depositing User: Derek Langford
Date Deposited: 18 Jan 2012 14:45
Last Modified: 22 Aug 2016 10:26
URI: http://repository.wit.ie/id/eprint/1699

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