A Visual Evaluation with Automate Devices by GR Reddy

By GR Reddy

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Central—Yellow light in the center of the bowl 2. g : macular degeneration). The patient should look in the center of the diamond formed by the four lights. 3. Large diamond—It is located below the central target and is used for patient with central scotoma who cannot see either central fixation light or small diamond. 2 4. Bottom LED—Some tests have points in the superior visual field that require a lower fixation light than the central target. The target used is the bottom LED of the large diamond.

This method is used in full threshold strategy. 24 A VISUAL FIELD EVALUATION WITH AUTOMATED DEVICES DETERMINATION OF THRESHOLD During determination of threshold at each point in the test grid, stimulus intensities will vary in such a way that some stimuli will be suprathreshold (brighter than necessary to elicit a response most of the time) and some will be infrathreshold (too dim to elicit a response most of the time). Threshold is thus bracketed by the stimuli as the examination proceeds. This method of bracketing is also known as staircase method for determining threshold.

The higher the number the greater the depature from the normal slope of hill of vision. CORRELATION BETWEEN PSD VALUE AND CONTOUR OF HILL OF VISION As you know the PSD is developed to express the irregular loss of retinal sensitivity - higher the irregularity in the loss of retinal sensitivity the higher the PSD value. When there is a localized field defect, the contour of field of vision is irregular without affecting the height of hill of vision (high PSD value) When there irregular generalized field defect, the height of hill of vision is decreased and the contour of hill of vision is irregular (high mean deviation index and high PSD value) When there is uniform generalized depression (the loss of retinal sensitivity at each point is identical), there is no dissimilarity in the loss of retinal sensitivity and hence the contour of hill of vision is smooth and the height of hill of vision is decreased (0 PSD and high mean deviation index).

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