PURPOSE. To determine the sensitivity and specificity for detecting glaucoma using GDx Access. Tjon-Fo-Sang and Lemij ( AJO, January 1997) were the first to demonstrate the sensitivity and specificity of NFL measurements in glaucoma using scanning laser polarimetry (GDx). They found a 96% sensitivity and 93% specificity while others have reported similar values. Some studies have reported lower findings. To date, no one has published a similar study using GDx Access.
METHOD. With previously established normograms supplied by the manufacturer, the sensitivity of the new commercially available GDx Access was assessed using 50 glaucomatous eyes, one from each of 50 subjects. The specificity was assessed using 50 normal eyes, one from each of 50 subjects. The relationship between mean deviation in the visual field and other parameters was also correlated with the nerve fiber layer defect as detected by the GDx Access of glaucomatous eyes. Normal subjects did not have any family history of glaucoma, had an intraocular pressure (IOP) of less than 20 and no ophthalmoscopic abnormalities. They had cupping of less than 0.5 with no difference of >0.2 between the eyes. Diagnostic criteria used to determine glaucomatous patients by at least two independent clinicians included IOP of > 20, repeatable, quantitative visual field defects, and relatively enlarged cup to disc ratio and cup asymmetry. Patients with questionable diagnoses, such as glaucoma suspects, and patients with non-repeatable visual fields were excluded from this study.
RESULTS. Under the conditions of this study in an urban-based population in New York City, the sensitivity of the GDx Access was 96% and the specificity was 94%.
CONCLUSIONS. The GDx Access appears to differentiate glaucomatous eyes from normal eyes in the vast majority of cases. The sensitivity of 96% and specificity of 94% is very similar to the findings of Tjon-Fo-Sang and Lemij using the standard GDx. The new GDx Access may prove to be a valuable tool in screening for glaucoma. This study did not address whether this technology is suitable for longitudinal follow up of patients with glaucoma.