Background: The aim of this study was to evaluate the ability of scanning laser polarimetry (SLP) parameters provided by commercially available GDx with variable corneal compensator (VCC) to discriminate between healthy and glaucomatous eyes.
Methods: Sixty-five healthy and 59 glaucomatous age-matched patients underwent a complete ophthalmological evaluation, an achromatic automated perimetry (AAP), and SLP with GDx-VCC. One randomly selected eye from each subject was considered. All glaucomatous eyes had reproducible visual field defects. Mean values (+/- SD) of all SLP-VCC parameters measured in the two groups were compared. Area under receiver operating characteristics (AUROC) curve and sensitivities at predetermined specificities of >or=80% and >or=95% for each single parameter were calculated. Moreover, the nerve fiber indicator (NFI) diagnostic accuracy was evaluated calculating positive, negative, and interval likelihood ratios (LRs) at different cutoff values.
Results: All SLP parameters were significantly different between the two groups (p<0.001). The NFI showed the best AUROC curve (0.938, SE 0.02) whereas temporal, superior, nasal, inferior, temporal (TSNIT) average was second best (0.897, SE 0.03), and normalized superior area was third (0.879, SE 0.04). At fixed specificity >or=95%, sensitivities ranged from 22% to 79.7% whereas for values >or=80%, sensitivities were in the 44.1-89.8% range. At a cutoff NFI value of 30, positive LR was 17.6 (95% CI: 5.8-53.6) and negative LR was 0.19 (95% CI: 0.11-0.33). Interval LRs for NFI showed that values <or=20 or >40 were associated with large effects on posttest probability.
Conclusions: SLP-VCC allows good discrimination between healthy and glaucomatous eyes. New software-provided parameters NFI, TSNIT average, and normalized superior and inferior areas appear to be reliable in the evaluation of glaucomatous disease. In particular, after evaluation on interval LRs, the NFI showed a high diagnostic accuracy for values <or=20 or >40.