Abstract
Abstract: :
Purpose: Ganglion cell loss may precede visual field loss in glaucoma (Kerrigan–Baumrind LA, Quigley HA, Pease ME, et al. IOVS 2000;41:741–8). Similarly, mild to moderate thinning of the retinal nerve fiber layer (RNFL), measured by scanning laser polarimetry (SLP), may not be associated with visual field loss (Reus NJ and Lemij HG, in press). In the present study, we compared SLP measurements of RNFL thickness in perimetrically unaffected eyes of glaucoma patients to eyes of healthy subjects. Methods: Thirty–five glaucoma patients with a reproducible visual field defect in one eye and a normal visual field in the other one (i.e. Glaucoma Hemifield Test, Within Normal Limits; mean deviation (MD), p>5%; pattern standard deviation (PSD), p>5%), and 73 age–matched healthy subjects were measured with the GDx VCC, a commercially available SLP (Laser Diagnostic Technologies, Inc., San Diego, CA, USA). The GDx VCC estimates RNFL thickness by measuring the summed retardation of a polarized laser beam induced by the birefringent RNFL; the instrument is equipped with individualized compensation of anterior segment birefringence. The MD and PSD of the glaucoma patients’ eyes with normal visual fields and the healthy eyes were not statistically significantly different (independent samples t test, p value, 0.22 and 0.16, respectively). We determined the statistical significance of differences in the GDx VCC parameters TSNIT Average, Superior Average, Inferior Average, TSNIT SD, and NFI between the two groups with independent samples t tests. Results: All GDx VCC parameters were statistically significantly different between the perimetrically unaffected eyes of glaucoma patients and the healthy eyes (TSNIT SD, p value, 0.007; other parameters, p value, <0.001). The NFI had a value ≥40 in 11/35 (31%) perimetrically unaffected eyes of glaucoma patients. This cut–off value reached a sensitivity and specificity of 85% and 96%, respectively, for detecting mild glaucoma (Zegers RHC, Reus NJ, and Lemij HG, submitted abstract for ARVO 2004). Conclusion: With the GDx VCC, RNFL thinning was detected in one third of perimetrically unaffected eyes of glaucoma patients.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • nerve fiber layer • clinical (human) or epidemiologic studies: prevalence/incidence