Abstract
Purpose: :
Schültze (1866) originally proposed that macular pigment (MP) could improve acuity by reducing the deleterious effects associated with the aberration of short–wave (SW) light. Although proposed well over a century ago, the hypothesis has never been empirically tested. We chose to begin evaluating the Acuity Hypothesis by measuring MP levels and gap acuity in the same observers.
Methods: :
40 young (average age = 20 yrs) healthy subjects were assessed. Peak MP density was measured using HFP in Newtonian view. Resolution acuity was measured as the minimum perceivable gap between two solid black lines (1’ width) vertically separated on a 0.5° circular backlit diffusing background. This background appeared either white (17 cd/m2) or yellow (16 cd/m2). The yellow background was produced by using LEDs with a peak = 570 nm. The white background was produced by combining the yellow with a blue LED (peak = 460 nm). The subject’s head (5.33 meters from the stimulus) was stabilized with a head–rest assembly and their adaptive state was controlled using a constant white surround (11 cd/m2).
Results: :
MPOD density ranged from 0.14 to 1.00 log units measured at 30’. Resolution acuities ranged from 14 to 75 arc seconds (M = 33 seconds). There was no significant relation between MPOD and resolution acuity as measured using the white or yellow background or the difference between the two.
Conclusions: :
MP passively filters SW light, which is known to be poorly focused at the plane of the retina. Our conditions were designed so that filtering by MP would influence the white condition, which contained SW light, but not the yellow condition, which did not contain SW light. Our finding that MP was not related to any of our conditions does not support the Acuity Hypothesis, as classically stated. Since standard acuity tasks reflect primarily high spatial frequencies, it is logically possible that a test designed to reflect mid–or–low spatial frequencies could yield different results.
Keywords: macular pigment • visual acuity