Abstract
Abstract: :
Purpose: To develop a technique for the measurement of the 2–D spatial profile of MPOD using visual displays and to test it in subpopulations of a supplementation trial with lutein (LUT) and zeaxanthin (ZEA), the constituents of the macular pigment (MP). Methods: An optical notch filter and a high brightness visual display produce two beams of light, one that is maximally absorbed by the MP (the test beam) and the other that remains virtually unaffected by it (the reference beam). A bright uniform background field is employed and the two beams are modulated sinusoidally in counterphase at 20 Hz. The test stimulus varies in size with distance away from fixation and is presented to the subject as a burst of flicker lasting for 500 ms. The luminance modulation depth of the reference beam remains constant (at 20%) whilst that of the test beam is adjusted in a staircase procedure to minimize the perception of flicker. When minimum flicker is achieved, the perceived brightness of the test stimulus matches that of the uniform surround. The use of sinusoidal modulation, small modulation depth, equiluminant "minimum flicker point", and short presentation time facilitate the setting of minimum flicker improving the accuracy of the estimates. Results: MPOD–profiles from –8° to +8° eccentricity were measured in 6 subjects on placebo and 5 subjects, who had been supplemented with 10mg LUT + 10mg ZEA for 6 months. The subjects were measured twice, first (T1) immediately after stopping supplementation and second (T2) 4 months after. At T1, there was a statistically significant (p=0.005) difference between the areas under the MPOD–profiles of the two groups with the larger area being that of the supplemented group while at T2, this difference had almost disappeared. Conclusions: The new technique provides an easy method to measure MPOD–profiles by making full use of the advantages of visual displays. The preliminary findings suggest that the amount of MPOD across the 16° eccentricity measured can be increased by supplementation with LUT and ZEA but appears to decrease after stopping supplementation.
Keywords: macular pigment • carotenoids/carotenoid binding proteins • clinical (human) or epidemiologic studies: systems/equipment/techniques