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HG Lemij, NJ Reus, TP Colen; GDx Measurements with Variable Versus Standard Cornea Compensation . Invest. Ophthalmol. Vis. Sci. 2002;43(13):260.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The Nerve Fiber Analyzer GDx (GDx; Laser Diagnostic Technologies, San Diego, CA, USA) is a scanning laser polarimeter that assesses retinal nerve fiber layer (RNFL) thickness by measuring the amount of birefringence of the RNFL. It has a standard compensation (SC) for anterior segment birefringence. SC may lead to spurious measurements1. A prototype GDx with variable compensation (VC) has been developed that can be adjusted to the individual eye. We compared measurements with SC and VC in healthy subjects and glaucoma patients. Methods: 66 eyes of 34 healthy subjects and 42 eyes of 31 non age-matched glaucoma patients were measured. For each eye, a mean of 3 high quality peripapillary scans was obtained with SC. The axis and magnitude of the anterior segment birefringence was determined from a mean of 3 measurements of the macular region, and used to set the VC. A mean of 3 high quality peripapillary images was then obtained. Results: The mean axis ( SD) and mean magnitude ( SD) of anterior segment birefringence of healthy eyes and of glaucomatous eyes was 19º nasally downward ( 14º) and 52nm ( 17nm), and 23º nasally downward ( 16º) and 45nm ( 11nm), respectively. Thickness and cross-sectional area parameters were significantly lower for VC than for SC in both groups. Ratio-based parameters were not statistically significantly different between VC and SC in either group. The range of thickness and cross-sectional area measurements was narrower for VC than for SC. It appeared that there was less overlap between normal and glaucomatous eyes with VC than with SC. Conclusion: Thickness and cross-sectional area parameters are significantly lower for VC than for SC in both healthy subjects and glaucoma patients. The apparently reduced overlap in measurements with VC between healthy subjects and glaucoma patients may improve the instrument's ability to separate normal from glaucomatous eyes. CR: F Support: The Rotterdam Eye Hospital Research Fund. The GDx with VC has been lent to us by the manufacturer. 1Greenfield, DS et al. Am J Ophthalmol 2000;129:715-722.
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