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M. Wall, C. A. Johnson, R. H. Kardon, D. P. Crabb; Use of a Continuous Probability Scale to Display Visual Field Damage. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1104.
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To derive and display the percentile score (1-99) at each perimetric location of a standard automated perimetry (SAP) test to determine if this technique will uncover patterns of loss not visible in standard (Statpac) probability maps.
We computed continuous scale probability plots from data collected from testing 305 normal participants with SAP using SITA Standard testing with Humphrey Field Analyzer (Model 750) automated perimetry. The thresholds from the results of the healthy subjects were sorted from highest to lowest at each visual field location tested. Empirical percentiles were derived in single increments from the first to the 99th percentile from age-corrected threshold decibel values from normal subjects. Using the statistical programming language R, we displayed the continuous probability plot as a color scale and then interpreted visual field plots from normal subjects and from patients with visual system disorders where the diagnosis was unequivocal.
Added information was achieved in identifying patterns of visual loss by using the 5th-20th percentile range in conjunction with the lower range below the 5th percentile typically used in visual field analysis software. Extent of contiguous regional defects appeared larger using this method. Normals commonly have threshold results within the 5-20 percentile range but test locations usually appeared spatially random throughout the visual field rather than in a pattern.
Continuous scale probability plots are a useful adjunct for interpretation of perimetry results.
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