Grading Bulbar Redness Using Cross-Calibrated Clinical Grading Scales

Abstract

To determine the between-scale agreement of grading estimates obtained with cross-calibrated McMonnies/Chapman-Davies (MC-D), Institute for Eye Research (IER), Efron, and Validated Bulbar Redness (VBR) grading scales. Modified reference images of each grading scale were positioned on a desk according to their perceived redness (within a 0 to 100 range) as determined in a previous psychophysical scaling experiment. Ten observers were asked to represent perceived bulbar redness of 16 sample images by placing them, one at a time, relative to the reference images of each scale. Only 0 and 100 were marked on the scale, but not the numerical position of the reference images. Perceived redness was taken as the measured position of the placed image from 0 and was averaged across observers. Overall, perceived redness depended on the sample image and the reference scale used (repeated measures ANOVA; P = 0.0008); six sample images had a perceived redness that was significantly different between at least two of the scales. Between-scale correlation coefficients of concordance ranged from 0.93 (IER vs. Efron) to 0.98 (VBR vs. Efron). Between-scale coefficients of repeatability ranged from five units (IER vs. VBR) to eight units (IER vs. Efron) of the 0 to 100 range. The use of cross-calibrated reference grades for bulbar redness grading scales allows comparison of grading estimates obtained with different scales. Perceived redness is dependent on the dynamic range of the reference images of the scale, with redness estimates generally being found to be higher for scales with a shorter dynamic range.