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Clemente Paz Filgueira, Elisa Colombo, Luis Issolio; Quantitative analysis of Visual Acuity and Threshold Contrast for induced scattering levels. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1067.
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© ARVO (1962-2015); The Authors (2016-present)
To study how visual acuity and contrast threshold are affected by different levels of scattering, considering the influence of glare. To analyze the relationship between the straylight parameter and contrast threshold.
In this work we performed measurements of corrected visual acuity (CVA), contrast threshold (Ct) based on a computerized system for visual function measurements (FVC100) and the straylight parameter (S) by means of CQuant. We covered a wide range of scattering through six experiment conditions: one free scattering condition and other 5 scattering conditions using single diffuser filters and combination of them. Measurements of CVA, S, Ct without glare and Ct with glare were performed for all 6 conditions. Ct was measured for spatial frequencies 1, 2, 4 , 8 and 12 cycles per degree, mean luminance of targets was 70cd/m2 and glare illuminance was set on 80lux. All measurements were replicated in three subjects with CVA=1 without filters.
Each Ct value is the average of three measurements. No scattering level caused significant drops in CVA, while they did caused the Ct to increase. We encountered that the best fitting between S and Ct was exponential (R2 higher than 0.90 for all spatial frequencies). We utilized the ratio between Ct with glare and Ct without glare as an indicator of the effect of glare and we found that the relationships between this ratio and S were lineal with positive slopes which increased according to spatial frequency increasing.
It is possible to reach normal VA under very elevated scattering conditions (equivalents to higher level of cataract development), in contrast with Ct which is, in fact, sensitive to changes in scattering levels. Correlations between Ct and S were high for all spatial frequencies, evidencing the FVC100 ability to detect changes in scattering levels. The more the scattering level and spatial frequency are, they cause more influence in glare measurements
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