Five young healthy subjects were evaluated. MP optical density (OD) was measured using HFP. Visibility was assessed by measuring contrast sensitivity thresholds at 8 cycles/deg (CST) using an optical system that passed xenon-light through the sine-wave grating. Blue haze was simulated using an ecologically valid broad-spectrum filter. Changes in MP density were simulated using a variable path length filter with an oil-based carotenoid solution that mimicked the absolute absorption spectrum of MP.
The average baseline CST was 0.004. Adding 0.25 OD of simulated MP lowered the average threshold to 0.003 (25%). An additional 0.25 OD decreased thresholds an additional 10%and the effect reached a plateau at about 0.50.
The largest improvement (about 25%) in contrast occurred with the initial, and relatively modest, addition of 0.25 OD units of simulated MP suggesting that the largest improvements may be linked to initial increases in MPOD.