Discrimination between normal and glaucomatous eyes with the Heidelberg retina tomograph (HRT-3) parameters and classification systems

Purpose:To diagnostic accuracy of HRT-3 parameters and to compare the Glaucoma Probability Score (GPS) with the Moorfields Classification (MFC) for discriminating between glaucoma and healthy eyes. Methods:240 POAG, 83 age matched control eyes were included. The gold standard for glaucoma diagnosis was a repeatable visual field defect (PSD with a p<5%, glaucoma hemifield test outside normal limits and a cluster of a minimum of 3 abnormal points with a p<5%, one of which with p<1%). Sensitivity, specificity, positive and negative likelihood ratios (LH+ and LH-) and area under the ROC curve (AROC) were the measures of diagnostic accuracy of HRT-3 global and regional stereometric, non stereometric and probability parameters. Glaucoma probability scores > 0.64 were considered as outside normal limits. Results:At 90% specificity, the highest sensitivities were found for vertical cup/disk ratio (75%), cup/disk area ratio (75%) and cup shape measure (specificity 95%, sensitivity 67%) and the AROC was respectively 0.90, 0.89 and 0.89. Among regional parameters the highest sensitivities were found for infero-temporal cup/disk area ratio (83%), infero-temporal cup shape measure (83%) and infero-temporal cup area (79%) with AROC respectively of 0.96, 0.92 and 0.91. The global GPS was found to have a 75% sensitivity at 90% specificity with an AROC of 0.88. Diagnostic accuracy was higher for global MFC (sensitivity 92%, Specificity 95%, LH+ 18.46, LH- 0.08) than for global GPS classification (sensitivity 77%, specificity 85%, LH+ 5.13, LH- 0.28). Among regional classification the highest diagnostic perforformances were found for infero- temporal MFC (sensitivity 73%, specificity 100%, LH- 0.27) and for infero-temporal GPS classification (sensitivity 75%, specificity 90%, LH+ 7.50, LH- 0.28). The agreement between MFC and GPS global and temporal classification was good (k=0.61 and 0.63 respectively, p<0.01) while for other regions of the optic disk was poor to moderate. Conclusions:The parameters with highest discriminating capability were vertical cup/disc and cup/disc area ratios and global cup shape measure. HRT-3 MFC showed the most accurate glaucoma classification both globally and regionally compared to the GPS. The agreement between the two classification system was found to be good only when considering the optic disk globally.