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Abstract #14026 Published in IGR 8-3
GDx-VCC performance in discriminating normal from glaucomatous eyes with early visual field loss
Da Pozzo S; Fuser M; Vattovani O; Di Stefano G; Ravalico GGraefe's Archive for Clinical and Experimental Ophthalmology 2006; 244: 689-695
BACKGROUND: To evaluate the ability of scanning laser polarimetry with variable corneal compensation (GDx-VCC) in separating healthy from glaucomatous patients with early visual field (VF) loss. METHODS: Sixty-two healthy and 48 glaucomatous age-matched patients with early glaucoma [mean deviation (MD): -1.74dB ± 1.69] underwent complete ophthalmological evaluation, automated achromatic perimetry (AAP) and retinal nerve fiber layer (RNFL) measurement with GDx-VCC. One randomly selected eye from each subject was considered. Glaucomatous VF defects had either Glaucoma Hemifield Test (GHT) outside normal limits or pattern standard deviation (PSD) outside 95% confidence limits. Mean ( ± SD) MD, PSD and GDx-VCC parameters in the two groups were compared by t-test. For each GDx-VCC parameter, area under receiver operating characteristics (AUROC) curve and sensitivity at predetermined specificity ≥ 80% and ≥ 95% were calculated. Moreover, the parameter with largest AUROC was evaluated by likelihood ratios (LRs). RESULTS: Mean values for MD, PSD and ten of 14 GDx-VCC parameters were significantly different between the two groups (P < 0.001). The three parameters with largest AUROCs were the nerve fiber indicator (NFI) (0.870), superior average (0.817) and normalized superior area (0.816) (P = 0.08 for differences between AUROCs). NFI displayed sensitivity values of 80.2% and 60.4% for specificity ≥ 80% and ≥ 95%, respectively. At NFI cutoff value of 30, positive LR was 34.9 (95% CI: 4.9-247.6) and negative LR was 0.45 (95% CI: 0.32-0.61). Interval LRs showed large effect on post-test probability for NFI values ≤ 18 or ≥ 31. CONCLUSIONS: In our sample of eyes with early VF loss, GDx-VCC showed moderate-to-good discriminating ability. Among the best performing parameters, NFI had the largest AUROC, but several glaucomatous eyes (21, 43.8%) had NFI < 30. This suggests that algorithm for NFI calculation requires some refinement when eyes with early VF loss are evaluated.
Dr. S. Da Pozzo, Eye Clinic, Ospedale Maggiore, University of Trieste, Piazza dell'Ospedale 1, 34129, Trieste, Italy. stefano34127@lycos.it
Classification:
6.9.1 Laser scanning (Part of: 6 Clinical examination methods > 6.9 Computerized image analysis)
