Comparison of the GDx VCC scanning laser polarimeter, HRT II confocal scanning laser ophthalmoscope, and stratus OCT optical coherence tomograph for the detection of glaucoma

Felipe A Medeiros, Linda M Zangwill, Christopher Bowd, Robert N Weinreb
Archives of Ophthalmology 2004, 122 (6): 827-37

OBJECTIVE: To compare the abilities of current commercially available versions of 3 optical imaging techniques: scanning laser polarimetry with variable corneal compensation (GDx VCC), confocal scanning laser ophthalmoscopy (HRT II [Heidelberg Retina Tomograph]), and optical coherence tomography (Stratus OCT) to discriminate between healthy eyes and eyes with glaucomatous visual field loss.

METHODS: We included 107 patients with glaucomatous visual field loss and 76 healthy subjects of a similar age. All individuals underwent imaging with a GDx VCC, HRT II, and fast retinal nerve fiber layer scan with the Stratus OCT as well as visual field testing within a 6-month period. Receiver operating characteristic curves and sensitivities at fixed specificities (80% and 95%) were calculated for parameters reported as continuous variables. Diagnostic categorization (outside normal limits, borderline, or within normal limits) provided by each instrument after comparison with its respective normative database was also evaluated, and likelihood ratios were reported. Agreement on categorization between methods (weighted kappa) was assessed.

RESULTS: After the exclusion of subjects with unacceptable images, the final study sample included 141 eyes of 141 subjects (75 with glaucoma and 66 healthy control subjects). Mean +/- SD mean deviation of the visual field test result for patients with glaucoma was -4.87 +/- 3.9 dB, and 70% of these patients had early glaucomatous visual field damage. No statistically significant difference was found between the areas under the receiver operating characteristic curves (AUCs) for the best parameters from the GDx VCC (nerve fiber indicator, AUC = 0.91), Stratus OCT (retinal nerve fiber layer inferior thickness, AUC = 0.92), and HRT II (linear discriminant function, AUC = 0.86). Abnormal results for each of the instruments, after comparison with their normative databases, were associated with strong positive likelihood ratios. Chance-corrected agreement (weighted kappa) among the 3 instruments ranged from moderate to substantial (0.50-0.72).

CONCLUSIONS: The AUCs and the sensitivities at high specificities were similar among the best parameters from each instrument. Abnormal results (as compared with each instrument's normative database) were associated with high likelihood ratios and large effects on posttest probabilities of having glaucomatous visual field loss. Calculation of likelihood ratios may provide additional information to assist the clinician in diagnosing glaucoma with these instruments.

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