Purpose: To evaluate the performance of the HRT II (Heidelberg retinal tomograph) and GDx (glaucoma detection) retinal nerve fibre analyzer in GDx when used in the primary care eye clinic setting for glaucoma screening.
Patients and methods: The study was prospective, cross-sectional, and hospital-based. One-hundred and twelve patients, 59 women and 53 men with a mean age of 57.8 years (range 18-85 years), had consecutive HRT II disc imaging and GDx retinal nerve fiber layer analysis. The Moorfield's regression classification and the 'GDx number' were used to predict the likelihood of glaucoma. A separate clinician, masked to the instrument results determined a definitive diagnosis, based on clinical examination. The extent of agreement between instrument prediction and the clinician diagnosis of glaucoma was examined by generating sensitivity and specificity tables.
Results: The HRT II had a sensitivity of 0.79 (95% CI: 0.60-0.92) and a specificity of 0.70 (95% CI: 0.60-0.78). The positive predictive value of the HRT II was 0.43 (95% CI: 0.29-0.57). Using a GDx number of 50 as 'cutoff' for glaucoma detection, the GDx had a sensitivity of 0.80 (95% CI: 0.59-0.93) and a specificity of 0.72 (95% CI: 0.61-0.80), with a positive predictive value of 0.43 (95% CI: 0.28-0.59).
Conclusions: For glaucoma detection, neither the HRT II nor the GDx are effective as stand-alone screening devices in the primary care setting.