Information Loss in 2 Bleb Grading Systems

Abstract

To assess the effectiveness of transferring descriptive information from bleb photographs to 2 recently described bleb grading systems: the Moorfields Bleb Grading System (MBGS) and the Indiana Bleb Appearance Grading Scale (IBAGS). Two experienced observers graded 51 clinical bleb photographs with a wide range of appearances using both the MBGS and IBAGS bleb grading systems in random order. Grading scores from the 2 observers were averaged, and these numbers used by a third investigator, who did not view the original photographs, to generate 102 sketched representations of the blebs. The sketches were labeled randomly, and 1 month later presented individually in random order, to mask which grading system was used as source data for each drawing. The original graders then used an arbitrary 1-5 scale to rate congruity between sketches and photographs for vascularity and morphology features, and overall agreement of the bleb sketches. For both the IBAGS and MBGS, interobserver agreement between the Congruity Scores (CS) of the 2 masked graders was excellent, ranging between 92% and 98% for each parameter. Overall CS results were 3.2 (good-very good) for IBAGS and 4.1 (very good-excellent) for MBGS. Vascularity CS scores from IBAGS were 3.0 (good) and those from morphology agreement averaged 3.5 (good-very good). For the MBGS, the respective results were 3.9 (good-very good) and 4.1 (very good-excellent), respectively. Photographic quality (P=0.012) and presence of a limbus-based conjunctival flap scar (P=0.012) had an influence on CS scores from IBAGS but not from MBGS. Both the IBAGS and MBGS produced acceptable agreement ratings between the sketches derived from grading system data and the original bleb photographs. These grading systems seem to adequately represent the blebs that are being encoded, without significant information loss from the simplification and translation process. The MBGS tended to have higher CS, and may be less influenced by photograph quality and bleb type, suggesting that bleb photographs may be best encoded for statistical analysis in clinical studies using this system.