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Gijs Thepass, Josine van der Schoot, Koenraad Vermeer, Hans Lemij; Comparison of Regression Analysis in structural and functional monitoring of glaucoma patients. Invest. Ophthalmol. Vis. Sci. 2013;54(15):2255.
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The agreement between structural and functional measurements in glaucomatous progression is generally poor. For Scanning Laser Polarimetry (SLP), the agreement with functional measurements has been explored relatively little. We wished to explore this in greater detail.
All eligible eyes of glaucoma patients from the Rotterdam Glaucoma Imaging Study with at least 5 follow-up measurements were enrolled (n=90) in this study. The average time between the first and last visit was 28 months (22-32). The proprietary progression programs for both SLP (GDx ECC, Carl Zeiss Meditec) and Standard Automated Perimetry (SAP) (Humphrey Field Analyzer II, 24-2 white on white SITA test program, Carl Zeiss Meditec) were used (GDx GPA Fast mode and HFA GPA, respectively). The GDx GPA flags any progression as possible or as likely. We also calculated linear regression coefficients for each series of measurements of the SAP Visual Field Index (VFI) and Mean Deviation (MD), and the GDx peripapillary retinal nerve fibre layer thickness (TSNIT average).
All results of the regression analyses are presented in Figs. 1 & 2. None of the tested eyes showed statistically significant progression by HFA GPA, but 5 (6%) eyes showed likely progression by GDx GPA (marked by red triangles in Figs. 1&2). Eight eyes (9%) showed TSNIT average increases (marked by green diamonds in figures 1&2). In our own regression analyses, 52 eyes (58%) showed disease progression by HFA VFI, 60 eyes (67%) by HFA MD and 49 eyes (54%) by GDx TSNIT average. In 31 eyes (34%), there was both structural and functional progression by HFA VFI and TSNIT average (see Figs.). Both structural and functional regression occurred in 18 eyes (20%).
Glaucomatous progression may be detected by SLP and by SAP. There was poor agreement between GDx and HFA progression, regardless of the used analysis. HFA GPA was more conservative than linear regression analysis. One of the limitations of this study is the relatively short average follow-up time. Plots that combine data from both structural and functional test methods (such as in Figs. 1 & 2) may help clinicians appreciate whether structural and functional measurements agree. In case of such agreement, they may feel more confident in their glaucoma management.
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