Purpose: A major factor limiting the visibility of distant targets is veiling attributed to atmospheric scattering, known commonly as haze. It has been suggested that yellow filters (in this case, the macular pigments, MPs) could selectively absorb this haze, thus extending visual range. This study is an empirical test of the visibility hypothesis.
Methods: Twelve subjects had their full contrast sensitivity function (CSF) (represented by six spatial frequencies) assessed in the presence of two background conditions: simulated blue haze and short wave–deficient light. Contrast sensitivity at the peak of the CSF (7.5 cycles per degree) was measured in the presence of the same two backgrounds as the full CSF, with the addition of a broadband xenon background condition in a separate sample of 25 subjects.
Results: Simulated blue haze was found to uniformly reduce the CSF in the 12 subjects for whom the full CSF was assessed. Therefore, only the peak was measured in the larger sample of 25 subjects. Macular pigment density was significantly related to energy at threshold for both the haze and xenon backgrounds but not the short wave–deficient background. Thus, subjects with higher levels of MP could withstand more light before losing sight of the target.
Conclusions: This result is consistent with previous modeling of the visibility hypothesis as well as visual range improvements seen when using an artificial MP filter.
Vision Sciences Laboratory, Psychology Department, University of Georgia, Athens, Georgia (all authors).
Laura M. Fletcher, Psychology Department, University of Georgia, 125 Baldwin Street, Athens, GA 30602, e-mail: email@example.com