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N.J. Reus, H.G. Lemij; Visualization of Localized Glaucomatous Defects with Scanning Laser Polarimetry . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3354.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Scanning laser polarimetry (SLP) estimates peripapillary retinal nerve fiber layer (RNFL) thickness by measuring the amount of retardation of a polarized laser beam induced by the birefringent RNFL. Two birefringent structures in the anterior segment, i.e. the lens and the cornea, also give rise to retardation. The GDx NFA (Laser Diagnostic Technologies, Inc., San Diego, CA, USA) cancels a fixed amount of retardation (fixed compensation, FC) to minimize their contribution to the signal. It has been shown that this may lead to spurious measurements due to large inter- and intraindividual variability in anterior segment birefringence. Compensating for an individual eye’s anterior segment birefringence (individualized compensation, IC) might allow a more accurate evaluation of the RNFL. We compared the visualization of localized glaucomatous RNFL defects in SLP images, with FC and with IC, to their visualization in red-free fundus photographs. Methods: Ten eyes of 6 glaucoma patients with localized, wedge-shaped, RNFL defects in red-free fundus photographs with matching visual field defects were imaged with a commercially available GDx VCC, equipped with an automated variable corneal compensator (VCC), and/or a GDx NFA modified to incorporate a manually operated corneal compensator (GDx prototype) (both from Laser Diagnostic Technologies, Inc., San Diego, CA, USA). Each eye’s anterior segment birefringence was estimated from a macular retardation profile that resulted from the interaction between the birefringence of the anterior segment and that of Henle’s fiber layer. Eight eyes were measured with the GDx prototype with FC and with IC and 4 eyes were measured with the GDx VCC. Retardation maps were superimposed on red-free fundus photographs, and visualization of the localized RNFL defects in the retardation maps was compared to that in the red-free fundus photographs. Results: Localized RNFL defects were visible in GDx retardation maps obtained with IC. The defects closely matched those observed in red-free fundus photographs. With FC, however, the GDx images did not correlate well with red-free fundus photography. Conclusions: With individualized compensation of anterior segment birefringence, SLP allows for accurate and objective assessment of localized glaucomatous RNFL loss.
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