The modified HRA used two-wavelength (488- and 514-nm) fundus AF,
15,25–28 based on the AF of lipofuscin, which is normally located in RPE cells.
29 To measure the MPOD, the dual-wavelength method compares results from excitation wavelengths that are differentially absorbed by the MPs, thereby taking into account the nonuniform distribution of lipofuscin in the RPE.
28 Several studies have found MPOD variability among different techniques and patients.
17,21,23,30,31 Lens opacity is a confounding factor, and since it was shown that cataract decreases MPOD measurement, only subjects with clear crystalline lenses were recruited in the present study.
32 The one-wavelength reflection method is a simplified method for measuring OD. Fewer studies have used reflectance of a single 460-nm wavelength.
16 Moreover, we do not know from the manufacturer which area is actually measured. It seems that this could change from one patient to another. Our MPOD values measured with the modified HRA were consistent with those found in the literature. In a normal population, some studies reported comparable MPOD values for the modified HRA: 0.44 ± 0.11 DU for 0.5° eccentricity and 0.11 ± 0.05 DU for 1.75° eccentricity (
n = 17; age range, 30 years)
26 ; 0.51 ± 0.12 DU at 0.5° eccentricity; 0.29 ± 0.07 DU at 2° eccentricity (
n = 14; age range, 56 years)
33 ; 0.50 ± 0.20 DU at 0.5° eccentricity (
n = 136; age range, 71 years)
17 ; and 0.24 ± 0.10 DU at 2° eccentricity (
n = 146; mean age, 71 years).
21 On the contrary, one of the few studies analyzing MPOD with the reflectance method by Visucam 200 has shown higher maximal MPOD values than what we have found in the present study: 0.62 ± 0.10 DU in pseudophakic eyes (
n = 22) and 0.67 ± 0.10 DU in phakic eyes (
n = 47) for maximum MPOD (mean age, 72 years).
16 In a more recent interventional study using the same technique, the baseline measurements before carotenoid supplementation were not provided.
11