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Jose J. Castro, Jose R. Jimenez, Carolina Ortiz, Aixa Alarcon, Rosario G. Anera; Visual Test For Quantifying Discrimination Capacity In Ocular Pathologies. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1891.
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To check a new visual test, designed as a software, for quantifying discrimination capacity under low-illumination conditions in patients with some ocular pathologies and to study the existence of a correlation between optical quality, as an objective measurement, and the discrimination capacity as visual function to evaluate visual performance.
We checked the test with two groups of observers: patients affected with keratitis and patients with age-related macular degeneration (ARMD). The test consists of the discrimination of luminous peripheral stimuli around a central high-luminance one over a dark background. The task of the subject is to press a button each time a peripheral stimulus is perceived. When the test is finished, the software gives a parameter, called visual-disturbance index, which quantifies the visual disturbances perceived by the observer. The disturbance index takes values of between 0 and 1, in such a way that the greater the index, the lower the discrimination capacity. We also took data from a visual-quality device based on the double-pass technique. We used the Strehl ratio, a parameter commonly used for estimating overall optical quality, which ranges from 0 to 1. A lower value of this parameter indicates that there is a greater contribution of the aberrations and ocular scattering and therefore poorer optical quality.
We found a significant descending correlation for the disturbance index as a function of the Strehl ratio in ARMD (r=0.85, p<0.05) and keratitis eyes (r=0.81, p<0.05). In both types of pathological eyes, the lower the Strehl ratio was, the higher the disturbance index was and, therefore, the lower the discrimination capacity was for peripheral stimuli, indicating a higher influence of different visual disturbances perceived by the observer due to the ocular pathology.
The visual test developed is a simple test available to any examiner to quantify visual disturbances under low illumination conditions by means of calculating the disturbance index in patients where visual performance is deteriorated. This test is more accurate than some questionnaires used to evaluate, qualitatively, visual disturbances. The effectiveness of the new visual test is reaffirmed by a significant descending correlation between the retinal-image quality and the visual disturbances perceived by the subject.
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