To compare the abilities of current commercially available versionsof 3 optical imaging techniques: scanning laser polarimetry with variablecorneal compensation (GDx VCC), confocal scanning laser ophthalmoscopy (HRTII [Heidelberg Retina Tomograph]), and optical coherence tomography (StratusOCT) to discriminate between healthy eyes and eyes with glaucomatous visualfield loss.
We included 107 patients with glaucomatous visual field loss and 76healthy subjects of a similar age. All individuals underwent imaging witha GDx VCC, HRT II, and fast retinal nerve fiber layer scan with the StratusOCT as well as visual field testing within a 6-month period. Receiver operatingcharacteristic curves and sensitivities at fixed specificities (80% and 95%)were calculated for parameters reported as continuous variables. Diagnosticcategorization (outside normal limits, borderline, or within normal limits)provided by each instrument after comparison with its respective normativedatabase was also evaluated, and likelihood ratios were reported. Agreementon categorization between methods (weighted κ) was assessed.
After the exclusion of subjects with unacceptable images, the finalstudy sample included 141 eyes of 141 subjects (75 with glaucoma and 66 healthycontrol subjects). Mean ± SD mean deviation of the visual field testresult for patients with glaucoma was −4.87 ± 3.9 dB, and 70%of these patients had early glaucomatous visual field damage. No statisticallysignificant difference was found between the areas under the receiver operatingcharacteristic curves (AUCs) for the best parameters from the GDx VCC (nervefiber indicator, AUC = 0.91), Stratus OCT (retinal nerve fiber layer inferiorthickness, AUC = 0.92), and HRT II (linear discriminant function, AUC = 0.86).Abnormal results for each of the instruments, after comparison with theirnormative databases, were associated with strong positive likelihood ratios.Chance-corrected agreement (weighted κ) among the 3 instruments rangedfrom moderate to substantial (0.50-0.72).
The AUCs and the sensitivities at high specificities were similar amongthe best parameters from each instrument. Abnormal results (as compared witheach instrument's normative database) were associated with high likelihoodratios and large effects on posttest probabilities of having glaucomatousvisual field loss. Calculation of likelihood ratios may provide additionalinformation to assist the clinician in diagnosing glaucoma with these instruments.