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Bartlett et al1 describe the clinical evaluation of the MPS 9000, which is designed to measure macular pigment optical density (MPOD) under clinical conditions. Their aim was to determine instrument variability (noise). Their conclusion, based on the coefficient of repeatability (COR), is that the instrument cannot reliably detect change less than 0.33 optical density (OD) units. This is poor and much worse than previous reports. There is a substantive literature illustrating the veracity of data generated by this instrument. It would have been helpful if the authors offered some comment on the discrepancy between their data and previous findings.
By extracting the raw data from figure 1 in Bartlett et al1 we have calculated the individual measurements for visits 1 and 2. In four out of 38 measurements, there is a difference of …