Purpose: By reducing rod intrusion and improving efficiency of neural signaling throughout the visual system, macular pigment (MP) could improve many aspects of visual performance in low-light level conditions. Our study examined this possibility for a variety of visual performance parameters, including spatial resolution, dark adaptation kinetics, and color detection.
Methods: Twenty-seven subjects participated in the study. Spatial profiles of MP optical density (MPOD) were determined by using heterochromatic flicker photometry. Mesopic- and scotopic-adaptation level experiments were conducted in Maxwellian view.
Results: Subjects with higher MPOD required significantly lower contrast to detect the mesopic-level resolution targets; this effect became stronger with increasing spatial frequency. Dark adaptation recovery times were significantly faster as a function of MPOD (by nearly 2 minutes for the lowest mesopic-level task [high versus low MPOD]; P < 0.001). Absolute scotopic thresholds were also significantly associated with MPOD (P < 0.001). Macular pigment optical density was inversely associated with detection of yellow (P < 0.001), and, paradoxically, approached a significant positive correlation with the detection of blue (P = 0.06).
Conclusions: Macular pigment appears to enhance visual function in low-light conditions. Based on the results of this study, it can be said that MP extends the range of foveal vision into lower light. Additionally, MP appears to enhance dark adaptation kinetics, which suggests that increased MPOD leads to more efficient photopigment regeneration. The findings of the color detection portion of the study are suggestive of an active compensatory mechanism that offsets absorption by MP in order to maintain normal color perception.