RESUMEN
BACKGROUND/AIMS: The MPS 9000 uses a psychophysical technique known as heterochromatic flicker photometry to measure macular pigment optical density (MPOD). Our aim was to determine the measurement variability (noise) of the MPS 9000. METHODS: Forty normally sighted participants who ranged in age from 18 to 50 years (25.4+/-8.2 years) were recruited from staff and students of Aston University (Birmingham, UK). Data were collected by two operators in two sessions separated by 1 week in order to assess test repeatability and reproducibility. RESULTS: The overall mean MPOD for the cohort was 0.35+/-0.14. There was no significant negative correlation between MPS 9000 MPOD readings and age (r=-0.192, p=0.236). Coefficients were 0.33 and 0.28 for repeatability, and 0.25 and 0.26 for reproducibility. There was no significant correlation between mean and difference MPOD values for any of the four pairs of results. CONCLUSIONS: When MPOD is being monitored over time then any change less than 0.33 units should not be considered clinically significant as it is very likely to be due to measurement noise. The size of the coefficient appears to be positively correlated with MPOD.