A Linear Discriminant Function to Improve the Glaucoma Probability Score to Distinguish Healthy From Glaucomatous Optic Nerve Head

Purpose:To create a linear discriminate function (LDF) formula by using the new Glaucoma Probability Score (GPS) global and sectorial optic nerve head (ONH) parameters measured by Heidelberg Retinal Tomograph 3 (HRT3, Heidelberg Engineering GmbH, Heidelberg, Germany) to improve the GPS diagnostic capacity to discriminate between healthy and glaucomatous eyes. Methods:233 eyes from 137 normal subjects and 96 glaucomatous patients were enrolled in this cross sectional study. All patients underwent a full eye examination, standard achromatic perimetry by using Humphrey Field Analyzer (Humphrey Inc, San Leandro, CA) and imaging with HRT3. Glaucoma was defined on the basis of SITA-24-2 visual field loss (PSD p<5% and Glaucoma Hemifield Test outside normal limits) on two consecutive visual fields. The area under the Receiver Operating Characteristics curves (AUC), sensitivity and specificity for different LDFs were analyzed as measures of diagnostic accuracy. The analysis was repeated after stratification for optic disc size. Results:When a LDF formula was generated by using only GPS parameters, the diagnostic capacity was 67%. However when GPS and standard stereometric parameters were used together, the LDF improved to 76%. In particular this LDF formula has been found to have a sensitivity of 85.5% and a specificity of 66% by using rim area, maximum cup depth, cup shape measure, GPS cup size, GPS cup depth and GPS horizontal retinal nerve fibre layer curvature. The GPS LDF AUC was 0.753 and its results were independent by the disc size. Conclusions:GPS diagnostic capacity has been found to have a high sensitivity and low specificity and to be disc size dependent (1), but using this new LDF formula, we improved the GPS capacity in glaucoma clinics.1. Oddone F et al: Exploring the Heidelberg Retinal Tomograph 3 Diagnostic accuracy across disc sizes and Glaucoma stages.