Measurement of Macular Pigment Optical Density: DensitometerTM versus MaculometerTM

Abstract

Purpose:: To compare the macular pigment optical density (MPOD) values obtained with two different heterochromatic flicker photometry (HFP) instruments, and to explore the implications of our findings with respect to the general principles of HFP methodology.

Methods:: We recruited 121 healthy subjects, 12 of whom were excluded due to an inability to use one or both HFP instruments. Demographic and health details were recorded. MPOD was measured using the two HFP instruments (the Eyemet Maculometer^TM and the Macular Metrics Densitometer^TM). The Maculometer^TM has a reference location at 5.5^o eccentricity and has a fixed flicker frequency (foveal target: 18 Hz and parafoveal target 13 Hz), whereas the Densitometer^TM has a reference location at 7^o and has the option to adjust flicker frequency.

Results:: The mean (± SD) MPOD measured with the Maculometer^TM was 0.394 (± 0.170), and that with the Densitometer^TM was 0.395 (± 0.189). The mean difference (± SD) in MPOD (Maculometer^TM-Densitometer^TM) was -0.001 (± 0.088). The 95% confidence interval for the mean difference was -0.018 to 0.016. For 50 of the 109 subjects (45.9%), the Maculometer^TM MPOD measurement was lower than that of the Densitometer^TM, for 5 subjects (4.6%) the readings were identical, and for 54 subjects (49.5%) the Maculometer^TM reading was higher. Regression of Maculometer^TM-Densitometer^TM difference on the variables age, gender, BMI, family history, and average MPOD produced the equation: diff = 0.127 - 0.002(age) - 0.122(average MPOD), the other variables not being significant at the 5% level (R² = 0.10).

Conclusions:: As the 95% confidence interval for the mean difference contains 0, we conclude that there is, on average, no difference in measurements provided by the two instruments. However, it appears from the regression analysis that the Maculometer^TM -Densitometer^TM difference becomes more negative the older the subject and/or the greater their MPOD.

Keywords: macular pigment • age-related macular degeneration • clinical research methodology