Macular pigment optical density measurement: a novel compact instrument

Abstract

A compact device to derive the optical density of human macular pigment (MP) using heterochromatic flicker photometry is described. The validity of the system is assessed by measuring the optical density spectra of MP in 12 healthy subjects and comparing this with well-established previously published values. The mean spectral absorbance characteristics of MP across subjects corresponds well with accepted values. As reported in other studies, our measurements show a wide variation of MP optical densities between individuals. In our technique within-subject variability is low; standard deviations are between 0.025 and 0.15 in most cases. The overall optical density of MP ranged from 0.08 to 0.84 with a mean of 0.496 and standard deviation of 0.257 at 460 nm. The stimulus size was 0.95 degrees. The unique feature of the technique is that it allows free viewing (not Maxwellian View) of the stimulus, it can be conducted easily and quickly and does not need frequent re-calibration.

Macular pigment assessment using a colour monitor

“…5 However, increasing clinical evidence for a link between MP and age-related retinal diseases has highlighted the epidemiological need for rapid, reliable noninvasive methods of measuring MP. 6,7 Here we pose the question: are the spectral emissions of the monitor phosphors themselves suitable stimuli for use in a flicker photometric estimation of individual MP complements? The phosphor spectra seem to be favorably placed, because the blue and green emissions peak, respectively, close to and remote from the macular pigment absorbance peak at 460 nm.…”

Measuring macular pigment optical density in vivo: a review of techniques

“…Given the complexity of these devices, operators need a significant amount of training [46]. As a result, several research groups have simplified the optics and allowed the use of a free view, or Newtonian view, setup [e.g., [46][47][48]62]. This negates the need for a bite bar, making the procedure more comfortable for the subject.…”

“…Since then, HFP has been developed and used by numerous research groups investigating macular pigment. Key papers incorporating detailed descriptions and variations of the technique include Hammond and Fuld [43], Hammond et al [44], Landrum et al [45], Wooten et al [46], Beatty et al [47], Mellerio et al [48], Bone and Landrum [49], Snodderly et al [50], Tang et al [62], Iannaccone et al [51], Stringham et al [52], and van der Veen et al [53]. All other studies using HFP to measure MPOD tend to use the instruments originally designed or developed by these investigators.…”

“…The wavelengths are chosen such that one is a short wavelength blue light that is maximally absorbed by macular pigment, and the other is a longer wavelength green to yellow light that is not absorbed by macular pigment [6]. If the colours are alternated at an appropriate frequency and the luminance of the two colours is not perceived to be equal by the subject, the stimulus will appear as a flickering light; the perceived colour of this light will be an amalgamation of the two source colours [47,49,50,63]. Typically, the radiance (often also termed intensity) of the blue light is adjusted by the subject until the observed flicker is minimized [e.g., 44-46, 48, 50, 52, 62].…”

“…Minimum motion photometry and apparent motion photometry [e.g., [37][38][39][40][41]. Heterochromatic flicker photometry [e.g., [42][43][44][45][46][47][48][49][50][51][52][53].…”