A Comparison of HRT II and GDx Imaging for Glaucoma Detection in a Primary Care Eye Clinic Setting

Abstract

Abstract: : Purpose: To evaluate the performance of the HRT II (Heidelberg retinal tomograph) and GDx (glaucoma detection) retinal nerve fiber analyzer in glaucoma detection when used in the primary care clinic setting for screening. Methods: A prospective cross-sectional hospital based study was performed on 112 patients referred by local optometrists. Consecutive HRT II disc imaging and GDx retinal nerve fiber layer analysis was performed on all subjects. The Moorfield's regression classification and the "GDx number" were used to predict the likelihood of glaucoma. A separate clinician, blinded to the instrument results determined a definitive diagnosis, based on clinical examination, including visual field analysis. The extent of agreement between instrument prediction and the clinician diagnosis of glaucoma was examined. Sensitivity and specificity tables were generated comparing the imaging devices to the clinical diagnosis. Results: The HRT II had a sensitivity of 0.86 (95% CI: 0.57-0.98) and specificity 0.76 (95% CI: 0.66-0.85) in right eyes. Similar findings were found in left eyes. The positive predictive value of the HRT II was 0.36 (95% CI: 0.20 -0.55). The GDx had a sensitivity of 0.92 (95% CI: 0.62-0.99) and a specificity of 0.52 (95% CI: 0.41-0.63) in right eyes, with a positive predictive value of 0.21 (95% CI: 0.11-0.35). Conclusions: As screening instruments for glaucoma detection, both the HRT II and GDx fail to met the criteria for a screening test. However our results do show that the HRT II is a more promising instrument.

Keywords: imaging/image analysis: clinical • optic disc