Abstract
Abstract: :
Purpose: Spatial distribution of the human macular pigment (MP) varies from a single central peak with a monotonic decrease towards higher eccentricities to distributions with a central peak surrounded by a ring of high density (Staurenghi et al. ARVO 2003). Intermediate distributions include partial rings and/or shoulders on the slopes of the profiles. We characterized the principal parameters of the MP distribution and investigated their relationship with age and sex. Methods: MP distribution was measured using the autofluorescence method (Delori et al. 2001) in 48 subjects with normal retinal status (F/M: 25/23; Ages: 24–75 years). Autofluorescence images with excitation at 470 and 550 nm (common barrier > 590 nm) were acquired with a modified fundus camera coupled to a CCD (12 bit grey levels). After alignment of the 2 images, the log ratio was calculated yielding the MP density distribution (with reference at 4° eccentricity). Results: Peak MP density at 460 nm was 0.56±0.18 D.U., independent of sex and age. The width of the distribution characterized by the eccentricity at 3/8 of peak was 1.4±0.3°, increasing with age by 8% per decade (p<0.001) and larger in women by 18% (p<0.001). The ring feature occurred over less than 1/3 of the perimeter of the distribution in 21 subjects (F/M=4/17), and in more than 2/3 of the perimeter in 18 subjects (F/M=14/4). Thus, women are more likely to exhibit the ring pattern than men (p=0.0002). The secondary maximum forming the ring (mean density: 80±11% of peak central density) occurred at an eccentricity of 0.79±0.14°; the minimum density (density: 71±12% of peak) between the central peak and the ring occurred at an eccentricity of 0.47±0.08°. The pattern of the MP distribution also corresponded to the pattern of the entoptically observed Maxwell spot (n=22, F/M=11/11, p=0.004). Conclusions: MP spatial distribution appears to be more complex than previously described in the literature. The ring feature can be subtle and may have been missed in noisier blue light reflectance images and by lower resolution psychophysical methods. Similar bimodal distributions of MP were observed in primate retinas (Snodderly, 1984). Individual variations in the MP distribution may be caused by variability in the amount of MP in the different retinal layers and in the anatomical dimensions of the foveal depression.
Keywords: macular pigment • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • retina