Macular pigment optical density measured by heterochromatic modulation photometry.

Cord Huchzermeyer,Tos T J M Berendschot,Jan Kremers,Juliane Schlomberg,Ulrich Welge-Lüssen,Joel Pokorny,William H Merigan

doi:10.1371/journal.pone.0110521

Abstract

PurposeTo psychophysically determine macular pigment optical density (MPOD) employing the heterochromatic modulation photometry (HMP) paradigm by estimating 460 nm absorption at central and peripheral retinal locations.MethodsFor the HMP measurements, two lights (B: 460 nm and R: 660 nm) were presented in a test field and were modulated in counterphase at medium or high frequencies. The contrasts of the two lights were varied in tandem to determine flicker detection thresholds. Detection thresholds were measured for different R:B modulation ratios. The modulation ratio with minimal sensitivity (maximal threshold) is the point of equiluminance. Measurements were performed in 25 normal subjects (11 male, 14 female; age: 30±11 years, mean ± sd) using an eight channel LED stimulator with Maxwellian view optics. The results were compared with those from two published techniques – one based on heterochromatic flicker photometry (Macular Densitometer) and the other on fundus reflectometry (MPR).ResultsWe were able to estimate MPOD with HMP using a modified theoretical model that was fitted to the HMP data. The resultant MPODHMP values correlated significantly with the MPODMPR values and with the MPODHFP values obtained at 0.25° and 0.5° retinal eccentricity.ConclusionsHMP is a flicker-based method with measurements taken at a constant mean chromaticity and luminance. The data can be well fit by a model that allows all data points to contribute to the photometric equality estimate. Therefore, we think that HMP may be a useful method for MPOD measurements, in basic and clinical vision experiments.

Highlights

The macula lutea (‘‘yellow spot’’), located in the central retina, derives its name from its yellowish appearance due to blue light absorption by the macular pigment (MP)
We used heterochromatic modulation photometry to measure macular pigment optical density and compared the results with those of two established methods: heterochromatic flicker photometry – a psychophysical method – and macular pigment reflectometry – a technique based on measuring light reflected from the retina
An augmented version of the model proposed by Pokorny, Smith and Lutze [15,17] was fit to the heterochromatic modulation photometry (HMP) data

Summary

Introduction

The macula lutea (‘‘yellow spot’’), located in the central retina, derives its name from its yellowish appearance due to blue light absorption by the macular pigment (MP). The latter consists of the carotinoids lutein and zeaxanthin[1,2,3] and absorbs short-wavelength light with a peak optical density at 460 nm [4]. The biological function is hypothesized to be a protection of the retina against phototoxicity by shielding against short-wavelength light [5], and by anti-oxidative effects [6,7]. Assessing the individual MPOD may have clinical relevance for estimating the individual protective effects. Large intra-individual variability of MPOD is relevant in psychophysical experiments because of variation in the available short-wavelength light at the receptoral level

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Results

Conclusion