An evaluation of a novel instrument for measuring macular pigment optical density: the MPS 9000

Authors

  • James Loughman,

    1. Macular Pigment Research Group, Dublin Institute of Technology, Optometry Department, College of Sciences & Health, Dublin, Ireland
    2. African Vision Research Institute, Faculty of Health Sciences, University of KwaZulu Natal, Durban, South Africa
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  • Grainne Scanlon,

    1. Macular Pigment Research Group, Dublin Institute of Technology, Optometry Department, College of Sciences & Health, Dublin, Ireland
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  • John M. Nolan,

    1. Macular Pigment Research Group, Waterford Institute of Technology, Waterford, Ireland
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  • Veronica O’Dwyer,

    1. Macular Pigment Research Group, Dublin Institute of Technology, Optometry Department, College of Sciences & Health, Dublin, Ireland
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  • Stephen Beatty

    1. Macular Pigment Research Group, Waterford Institute of Technology, Waterford, Ireland
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James Loughman
Optometry Department
Dublin Institute of Technology
College of Sciences & Health
Kevin St
Dublin 8
Ireland
Tel: + 353 1 4022841
Fax: + 353 1 4024915
Email: james.loughman@dit.ie

Abstract.

Purpose:  Of the antioxidants found in the human retina, only the macular carotenoid quantities can be estimated noninvasively (albeit in a collective fashion), thus facilitating study of their role in that tissue. The aim of this study was to evaluate concordance between macular pigment optical density (MPOD) values recorded on a commercially available instrument, the MPS 9000, with those of an already validated heterochromatic flicker photometry instrument. Also, we assessed and compared test–retest variability for each instrument.

Methods:  Macular pigment optical density at 0.5 retinal eccentricity was measured using two different heterochromatic flicker photometers, the MPS 9000 and the Macular DensitometerTM, in 39 healthy subjects. Test–retest variability was evaluated separately for each instrument by taking three readings over a 1-week period in 25 subjects.

Results:  There was a moderate positive correlation for MPOD at 0.5° of retinal eccentricity between the MPS 9000 and the Macular Densitometer described by the linear equation y = 0.763x + 0.172 (r = 0.68, p < 0.001, r2 = 0.46); however, a paired-samples t-test showed a significant difference in terms of mean values, with a bias of lower MPOD values being yielded by the MPS 9000 (t = −4.103, p < 0.001). Bland–Altman analysis indicated only moderate agreement between the two instruments, reflected in 95% limits of agreement of 0.1 ± 0.27. Inter-sessional repeatability, expressed as a coefficient of repeatability, ranged from 0.18 to 0.21 [mean (±SD): 0.19 (0.02)] for the MPS 9000 and from 0.11 to 0.12 [mean (±SD): 0.12 (0.01)] for the Macular Densitometer.

Conclusion:  The results demonstrate that the MPS 9000 consistently yields MPOD readings, which are lower than that found with the Macular Densitometer, and exhibits substantial test–retest variability.

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