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A. P. Ginsburg, S. V. Subramaniam; Effect of Simulated Haze and Glare on Visual Acuity and Contrast Sensitivity: A Comparison. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4457.
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Visual acuity (VA) remains the standard measure of testing in many clinical scenarios such as correction of refractive error, assessing vision loss in cataract, evaluating improvement in vision following cataract surgery or refractive surgery. The ability to resolve black-on-white letters in a visual acuity chart is regarded as a measure of visual function. In reality, a visual scene with 100% contrast is rarely encountered. For this reason, a patient with 20/20 vision may still have trouble in everyday low contrast situations such as face recognition or night driving. Contrast sensitivity (CS) tests the threshold contrast required to distinguish a target from the background. Sine-wave gratings are used in a range of spatial frequencies to obtain a contrast sensitivity function for the visual system. The purpose of this study is to compare the amount of change in VA with change in CS under simulated haze and glare conditions.
VA and CS were measured in the dominant eye of 10 subjects with no ocular abnormalities and BCVA of 20/20 or better under normal, haze and glare conditions. Haze was simulated by haze glasses with a light scattering material and glare was produced by Mentor Brightness Acuity Tester (BAT). VA was measured using the ETDRS chart while CS was measured at 6 and 12 cycles per degree (cpd) using FACT (Vision Sciences Research Corp., San Ramon, CA). This is a 3-AFC test in which the sine-wave gratings in decreasing contrast steps are oriented either vertical, 15° to the right or left.
Mean VA was greater than 20/20 under all conditions, averaging -0.08±0.04 under normal, -0.03±0.07 with glare and -0.03±0.08 under haze conditions. Mean CS loss at 6 and 12cpd was functionally significant and exceeded 0.3 log units under conditions of haze, averaging 0.59±0.15 at 6cpd and 0.80±0.23 at 12cpd. Loss in VA ranged from no loss to one-line loss under glare and haze while loss in CS in the same subjects ranged from 0.38 to 0.87 log units at 6 cpd and from 0.6 to 1.17 log units at 12 cpd as measured by FACT.
VA can show minimal to no loss in acuity even when a patient is experiencing decreased quality of vision as in glare and haze. Contrast sensitivity is a more sensitive test of the functional quality of vision and adds a wealth of information that is masked by testing VA alone.
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