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ARTHUR A. EASTMAN, SYLVESTER K. GUTH, GERHARD A. BRECHER; Instrument With Variable Beam Splitter For Measuring Contrast Sensitivity. Invest. Ophthalmol. Vis. Sci. 1963;2(1):37-46. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
A versatile instrument is described which permits studying many parameters of visibility thresholds, such as contrast sensitivity of test targets which are lighter than their backgrounds and of test targets which are darker than their backgrounds. The use of a single method, as in this device, eliminates the problems encountered when one compares apparently conflicting data obtained with various methods based on different principles. A collimated beam of light is split into two beams by means of a mirror with varying degrees of reflection and transmission (gradient, optical wedge). The luminous flux of the two beams can be altered, separately in order to change the luminance of test targets and their background. The factors which can be varied independently are: target size, target pattern, hues of target and background, exposure time, stimulus location on the retina, size of field of view and binocular or monocular exposure. In exploratory experiments contrast was studied with two test targets of equal luminance surrounded by two backgrounds of different luminance (test of Ewald, Hering). By varying the luminance of one target the subjective brightness of the two targets was matched. This gave a measure of the intensity of the physiological contrast phenomenon. A decrease in exposure time of the test targets and their backgrounds from 10,000 msec, to about 50 msec, enhanced, the phenomenon of physiological contrast.
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