Improving the repeatability of heterochromatic flicker photometry for measurement of macular pigment optical density.
BACKGROUND
Heterochromatic flicker photometry (HFP) is a psychophysical technique used to measure macular pigment optical density (MPOD). We used the MPS 9000 (MPS) HFP device. Our aim was to determine if the repeatability of the MPS could be improved to make it more suitable for monitoring MPOD over time.


METHODS
Intra-session repeatability was assessed in 25 participants (aged 20-50 years). The resulting data was explored in detail, e.g., by examining the effect of removal and adjustment of data with less than optimal quality parameters. A protocol was developed for improved overall reliability, which was then tested in terms of inter-session repeatability in a separate group of 27 participants (aged 19-52 years).


RESULTS
Removal and adjustment of data reduced the intra-session coefficient of repeatability (CR) by 0.04, on average, and the mean individual standard deviation by 0.004. Raw data observation offered further insight into ways of improving repeatability. The proposed protocol resulted in an inter-session CR of 0.08.


CONCLUSIONS
Removal and adjustment of less than optimal data improved repeatability, and is therefore recommended. To further improve repeatability, in brief we propose that each patient perform each part of the test twice, and a third time where necessary (described in detail by the protocol). Doing so will make the MPS more useful in research and clinical settings.
Ophthalmic Research Group, School of Life and Health Sciences, Aston University, Birmingham B4 7ET, UK.
Olivia
O
Howells
Frank
F
Eperjesi
Hannah
H
Bartlett
D000328:Adult; D003720:Densitometry; D003941:Diagnostic Techniques, Ophthalmological / Q000592:standards*; D005260:Female; D006801:Humans; D014975:Lutein / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D010783:Photometry / Q000295:instrumentation*; D012016:Reference Values; D015203:Reproducibility of Results; D012160:Retina / Q000378:metabolism*; D012168:Retinal Pigments / Q000378:metabolism*; D024341:Xanthophylls / Q000378:metabolism*; D055815:Young Adult; D065146:Zeaxanthins
D012168:Retinal Pigments; D024341:Xanthophylls; D065146:Zeaxanthins; D014975:Lutein