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SA Kabanarou, C Bellmann, MD Crossland, LE Culham, EM Fine, GS Rubin; Psychophysical Mapping of the Blind Spot: A Validation Study . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3806.
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Purpose: Precise mapping of the visual field in persons with age-related macular degeneration (AMD) has required a scanning laser ophthalmoscope (SLO) or other device to control for eye movements. SLOs are not readily available, nor practical for routine clinical use. It is possible to use the physiological blindspot as an eye position marker, and thus assure accurate fixation. To do this, one must develop a technique for mapping the blindspot. Here we compare different techniques for mapping the blindspot with monocular and binocular viewing. Methods: 10 individuals aged 20-35 years with normal vision and no known ocular pathology were tested with three different experimental techniques to map their blind spots with respect to fixation. Monocular mapping was performed with and without control of fixation using an SMI EyeLink eye tracker. The blind spot was also mapped during binocular viewing using CrystalEyes shutter glasses. Horizontal and vertical distances from centre of fixation were compared. Results: The average horizontal distances from fixation to the centre of the blind spot were 16.6 ± 0.9 deg and 15.9 ± 1.52 deg for monocular tests with and without control of fixation, respectively, and 16.1 ± 1.7 deg for the binocular test. The differences were not statistically significant by repeated-measures ANOVA. The average vertical distances were 1.54 ± 0.8 deg, 1.81 ± 0.7 deg, and 1.98 ± 0.7 deg inferior to fixation (difference significant, p< .05). Posthoc comparisons revealed that the vertical distance was displaced inferiorly 28 minarc with binocular viewing compared to monocular viewing with controlled fixation (p < .05). Conclusion: There was close correspondence among the different mapping techniques. Although the determined centre of the blind spot was vertically displaced during binocular viewing, the discrepancy was less than 0.5 degrees of visual angle. These techniques can now be used to compare the size and location of the physiological blind spot mapped using psychophysical measures and actual blind spot imaged with an SLO.
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