EXTENDED REPORT

Accuracy of GDx VCC, HRT I, and clinical assessment of stereoscopic optic nerve head photographs for diagnosing glaucoma

Nicolaas J Reus, Maartje de Graaf and Hans G Lemij

Glaucoma Service, The Rotterdam Eye Hospital, Rotterdam, The Netherlands

Correspondence to:
Correspondence to:
N J Reus
The Rotterdam Eye Hospital, P.O. Box 70030, NL-3000 LM Rotterdam, The Netherlands;reus{at}oogziekenhuis.nl

Aims: To determine and compare the accuracy and reproducibility of GDx variable cornea compensation (VCC) scanning laser polarimetry (SLP) with VCC, Heidelberg retina tomograph (HRT) I confocal scanning laser ophthalmoscopy (CSLO), and clinical assessment of stereoscopic optic nerve head (ONH) photographs for diagnosing glaucoma.

Methods: One eye each of 40 healthy subjects, 48 glaucoma patients, and six patients with ocular hypertension were measured with SLP-VCC and CSLO. Simultaneous stereoscopic ONH photographs were also obtained. Sixteen photographs of healthy and glaucomatous eyes were duplicated for assessing intraobserver agreement. Four glaucoma specialists, four general ophthalmologists, four residents in ophthalmology, and four optometrists classified the ONH photographs as normal or glaucomatous. For SLP-VCC, the nerve fiber indicator (NFI) was evaluated. For CSLO, the Moorfields regression analysis (MRA) and the Bathija linear discriminant function (LDF) were used. Sensitivity, specificity, percentage of correctly classified eyes, and intra- and interobserver agreement, expressed as kappa () were calculated.

Results: SLP-VCC had the highest diagnostic accuracy, with a sensitivity, specificity, and overall correct classification of 91.7%, 95.0% and 93.2%, respectively. CSLO, expressed as Bathija LDF and MRA, had a diagnostic accuracy comparable to glaucoma specialists and general ophthalmologists with an overall accuracy of 89.8%, 86.4%, 86.7% and 85.2%, respectively. Residents classified the fewest eyes correctly. Intraobserver agreement for classifying the ONH photographs ranged between 0.48 (within residents) and 0.78 (within glaucoma specialists). The interobserver agreement ranged between 0.45 (between residents) and 0.74 (between glaucoma specialists). The agreement between observers and CSLO MRA (, 0.68) was statistically significantly higher (p<0.001; paired t-test) than between observers and SLP-VCC NFI (, 0.60) and CSLO Bathija LDF (, 0.62).

Conclusion: Automated analysis of measurements with GDx VCC and HRT had a similar diagnostic accuracy for glaucoma as classification of stereoscopic ONH photographs by glaucoma specialists, thus bringing all eye-care professionals to this desirable level. The intra- and interobserver agreement for ONH analysis was only moderate to good. We think these imaging techniques may assist clinicians in diagnosing glaucoma.

Abbreviations: AUC, area under curves; CSLO, confocal scanning laser ophthalmoscopy; GHT, glaucoma hemifield test; HAP, Hodapp-Anderson-Parrish; HRT, Heidelberg retina tomograph; IOP, intraocular pressure; LDF, linear discriminant function; MRA, Moorfields regression analysis; NFI, nerve fiber indicator; OHT, ocular hypertension; ONH, optic nerve head; REH, Rotterdam Eye Hospital; RNFL, retinal nerve fiber layer; ROC, receiver operating characteristic; SLP, scanning laser polarimetry; VCC, variable cornea compensation

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