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M. Sillero Quintana, A. Langa, I. del Moral–Martínez, M.J. Perez, M.C. Puell, C. Sanchez–Ramos; Polarized Filters Enhance Contrast Sensitivity When Glare Is Produced On A Flat Surface Under Photopic Conditions . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1225.
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To evaluate the effects of glare on contrast sensitivity under photopic conditions, we projected a collimated light beam onto each letter of a Pelli–Robson contrast sensitivity chart. This method differs from most reports in the literature, in which glare is generated by a diffuse light source, eccentric to the test target. Our ecological approach achieved controlled yet realistic, polarized reflected glare on the test surface, which prevents subjects from properly seeing the letters. This scenario represents the real conditions of dazzling when subjects view targets on horizontal surfaces with the sun in their eyes (such as during driving or fishing).
Subjects of different age (n = 107; averaged age = 37.34; SD = 21.8) with normal vision (averaged visual acuity Snellen coefficient = 0.96; SD = 0.27) performed the test, seated with their head placed on a chin–rest located 1.76 meters away from the test, which was placed on the floor. Binocular contrast sensitivity was recorded with the subject wearing spectacles fitted with a standard polarized filter, with coloured filter, and without spectacles. The dazzling light hit the test surface first at an angle of 31.5º with respect to the horizontal (Brewster angle) and then at 46.6º, 37.6º, 23.8º and 17.2º. Both the visual and angle conditions were randomized to avoid glare, tiredness and memorization effects on the results.
The graph shows how the effect of glare was neutralized by the polarized filter –with values close to reference levels without glare recorded– but not by the coloured filter, which gave rise to similar contrast sensitivities as for the uncovered eyes. The benefits of polarized filters were reduced –but were still significant– as the angle of incident light was varied from the Brewster angle.
Our results in physiologically terms indicate the benefits of using polarized filters to improve contrast sensitivity in the presence of glare produced on a horizontal surface under photopic light conditions.
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