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

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 Densitometer^TM, 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.