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P. Gunvant, R. Gurses-Ozden, K. Soules, Q. Zhou, B. Lo, Y.-J. Duh, GDx ECC Normative Database Study Group.; Comparison of RNFL Obtained Using GDx-VCC & ECC Algorithms and Its Correlation With Visual Field Indices. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4399.
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To compare the retinal nerve fiber layer (RNFL) measurements obtained by the GDx-Variable Corneal Compensator (VCC) and GDx- Enhanced Corneal Compensator (ECC) algorithms and to correlate the GDx RNFL thickness measurements with standard automated perimetry (SAP) mean deviation (MD) parameter.
Healthy and glaucomatous subjects were enrolled in 10 international sites. Subjects underwent three GDx scans with both VCC & ECC algorithms and SAP testing using Humphrey Visual Field Analyzer. The mean difference and standard deviation (SD) between the VCC and ECC measurements were calculated. The correlation between the GDx RNFL measurements and MD were studied.
Four hundred thirty one eyes of 431 subjects were enrolled (243 healthy and 188 glaucomatous). The Mean and SD for age, MD, PSD and GDx parameters are presented in Table 1. The Mean RNFL measurements and SDs were significantly different between the VCC and ECC in the inferior quadrant for the healthy group (p=0.001, and p=0.02, respectively) and nasal and temporal quadrants for both healthy group and glaucomatous group (p<0.001 for all measurements). There was a moderate correlation between ECC RNFL thickness values and MD of glaucomatous participants for TSNIT, Superior and Inferior average (r= 0.51, 0.44, 0.49 respectively) with overall correlation in ECC values being better than VCC values (r=0.45, 0.43, 0.40 respectively). The correlation between MD and Inferior Average was r=0.49 for ECC versus 0.40 for VCC which was significantly different (p=0.01, paired t-test).
There is a small but a statistically significant difference between GDx VCC and ECC RNFL measurements. Moreover, the variance is lower in various quadrants for ECC measurements when compared to VCC measurements. This may point to a slightly better correlation of GDx ECC RNFL measurements with visual field indices.
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