Abstract
Purpose::
To measure macular pigment (MP) profiles over periods of several years in order to monitor possible underlying fluctuations in MP levels and to assess the reliability of repeated assessments based on the psychophysical technique of minimum motion photometry.
Methods::
Serial MP spatial distribution profiles were obtained in 4 healthy subjects (A - D) over periods of between 5 and 9 years using the minimum motion paradigm. A square wave grating (460nm vs 580nm) was moved at constant horizontal velocity (37 deg/sec) within 2 circular fields (radius 0.45° and 1.1°) and 11 annular segments (maximum radius 7.4°). The radiance of the 580nm stimulus was adjusted to minimize the perceived motion. Relative optical density (OD) was computed from log (Rref/R), where Rref is the mean radiance setting for the three most eccentric locations (5.5°, 6.6° and 7.4°) and R is the radiance setting at any location.
Results::
The shapes of MP profiles varied in a way representative of a normal population and can be described by a logistic, exponential or polynomial function. Mean peak MPOD values ranged from approximately 0.15 to 0.8 and the lateral extent (OD<0.04) ranged from 1.7° to 5.3°. Standard deviations correlated both with the amount of moving boundary in the field and with the gradient of MPOD reduction computed over different eccentricities. Linear regression through serial data points (2° circular field) measured over a period of 9 years gave gradients of 0.01 (A) and 0.007 (B); over 5 years gradients were 0.02 (C) and -0.0064 (D). Gradients were lower at almost every other eccentric retinal location.
Conclusions::
This study demonstrates the long-term stability of MPOD at different retinal locations over periods of up to 9 years. Measures of peak OD and MP distribution show a high degree of inter-session consistency and indicate intra-session reproducibility that is eccentricity-dependent. Greatest intra-session measurement errors occur at retinal locations associated with the steepest gradient of MP change. The findings provide an assessment of stability that is pertinent to studies that aim to modify MP profiles through dietary supplementation, monitor the possible role of MP in ARMD or track seasonal or age-related changes in MP.
Keywords: macular pigment • carotenoids/carotenoid binding proteins • clinical (human) or epidemiologic studies: systems/equipment/techniques