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Emily R. Bovier, Laura M. Fletcher, Michael Engles, Billy R. Hammond, Jr.; The Contrast Sensitivity Function Measured under Blue Haze Conditions. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4806. doi: https://doi.org/.
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The contrast sensitivity function (CSF) is often measured under laboratory conditions that may not adequately reflect spatial vision measured using light sources that are typical of vision outdoors. For example, one factor that has been shown to limit visual range is blue-haze (preferential scatter of short-wave light). In this study, we simulated blue haze by combining xenon-white light with a filter designed to match standard atmospheric measures. The CSF was measured using transparency gratings in a Maxwellian optical system while simulated blue haze was imposed between the target and the eye of the observer. This provided a CSF curve as would be obtained when viewed through air light and at a distance.
A three-channel optical system with a 1000-W xenon arc bulb light source was used to evaluate the CSF using sinusoidal gratings presented at 2, 4, 8, 15, 22, and 43 cycles/degree under simulated blue haze (BH) conditions. CSF was also measured under short-wave deficient (SWD) conditions to determine whether it was the short-wave scatter itself that was degrading the CSF when measured under broad-band conditions. Thresholds for each condition were determined using a two-alternative forced choice staircase method.
The CSF measured under BH and SWD conditions had the characteristic unimodal shape often derived in laboratory settings. Despite matched luminance, however, the CSF measured under BH conditions was significantly reduced compared to the SWD condition (area under the curve: t = 7.77, p < 0.05). This reduction was uniform and did not differ across spatial frequencies, F(5, 42) = 0.541, p = 0.744.
The results indicate that the detectability of targets of varying spatial frequency is uniformly depressed in the presence of simulated blue haze. Comparison to the CSF measured by removing just the short-wave portion of the light showed that, despite correcting for luminance differences, the "blue" light was responsible for this reduction.
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