Abstract
Purpose: :
A potentially major factor limiting the detectability of distant targets is veiling due to atmospheric light scattering, known commonly as haze. Under typical conditions, atmospheric haze is shortwave dominant (peak = 460nm), hence its name, Blue Haze. Wooten & Hammond (2002) first modeled the influence of a yellow filter (in this case, the macular pigments, MP) that absorbs blue haze, thus conferring a visual benefit (i.e., observers can, theoretically, see farther). The purpose of this study was to begin to characterize the influence of MP on target detectability under simulated blue haze and achromatic (i.e., "sunlight") conditions.
Methods: :
Three experienced subjects participated in this study. A two-channel Newtonian view optical system was used to present a 0.5-deg, 3.36cpd shortwave deficient target (cutoff = 570nm) at 2.5cd m-2. Superposed onto the target was a background (either a 582nm interference filter, a blue haze filter or an "unfiltered" xenon) whose luminance was under experimenter control. Targets were viewed binocularly. Alternating ascending (5) and descending (5) thresholds were obtained via the method of limits. Threshold was taken to be the average of the background luminance at each of the 10 transition points for each condition. Macular pigment optical density (MPOD) was measured in each subject’s right eye using heterochromatic flicker photometry.
Results: :
Visual benefit for the blue haze and achromatic conditions (affected by MP absorption) was calculated as the ratio of the threshold in each condition to the threshold obtained using the 582nm background (unaffected by MP absorption). The mean MPOD for our subjects was 0.72±0.12. The mean visual benefit for the blue haze and achromatic background conditions was 2.09±0.01 and 1.6±0.19.
Conclusions: :
These preliminary data indicate a significant relation between MP and visibility measured under these varying conditions. Additional data will be presented.
Keywords: macular pigment • retina