Position Index for a Glare Source in the Whole Visual Field

Abstract

The objective of this research work is to propose a Position Index of glare sources in the whole visual field. The Guth Position Index has an issue that it does not define glare sources below the line of sight.Our first experiment to investigate the visual field was conducted using the Goldmann Perimeter. Twenty-five observers aged from 20 to 47 participated in the experiment. Their average visual field is presented by five isopters (lines joining points of equal sensitivity on a visual field chart). These isopters show that visual sensitivity has a higher value at positions below the line of sight than above. The second experiment to assess the subjects’ sensitivity to glare was conducted using a Glare Testing Instrument made for this research. Equal glare sensitivity curves were obtained from the tests. The shapes of the equal glare sensitivity curves and those of the isopters are interrelated at positions above the line of sight. However, at positions below the line of sight, the shapes of the equal glare sensitivity curves are wider than those of the isopters. Therefore, extending the Guth Position Index to positions below the line of sight according to the isopters is inadequate. A new position index chart was derived from the equal glare sensitivity curves. In the whole visual field, the position index could be determined from the new chart.