Vistech

A clinical test for contrast sensitivity. It consists of a chart containing five horizontal rows, each with nine circular patches of sinusoidal gratings. The gratings are either vertical or 15º to the right or to the left. Each row has a different spatial frequency, starting from the top of the chart: 1.5, 3.0, 6.0, 12.0 and 18.0 cycles per degrees when viewed at a distance of 40 cm. The contrast level of each of the nine gratings decreases from 33% to 0% from left to right in approximately 0.2 log unit steps. The patient is asked to look along each row, identifying the orientation of the grating. The testing is carried out monocularly with optical correction, if any. The last grating of each row that is incorrectly identified is noted on an evaluation form, which is provided with the test. The end points of each of the five rows are connected to form a contrast sensitivity curve for each patient. It is then compared with normal values indicated on the form. There is also a version for testing at distance. Syn. Vision Contrast Test System (VCTS). See contrast sensitivity chart; Arden grating test.

单词	vistech
释义	Vistech Vistech A clinical test for contrast sensitivity. It consists of a chart containing five horizontal rows, each with nine circular patches of sinusoidal gratings. The gratings are either vertical or 15º to the right or to the left. Each row has a different spatial frequency, starting from the top of the chart: 1.5, 3.0, 6.0, 12.0 and 18.0 cycles per degrees when viewed at a distance of 40 cm. The contrast level of each of the nine gratings decreases from 33% to 0% from left to right in approximately 0.2 log unit steps. The patient is asked to look along each row, identifying the orientation of the grating. The testing is carried out monocularly with optical correction, if any. The last grating of each row that is incorrectly identified is noted on an evaluation form, which is provided with the test. The end points of each of the five rows are connected to form a contrast sensitivity curve for each patient. It is then compared with normal values indicated on the form. There is also a version for testing at distance. Syn. Vision Contrast Test System (VCTS). See contrast sensitivity chart; Arden grating test.
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