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Amir Marvasti, Renato Lisboa, Linda Zangwill, Robert Weinreb, Felipe Medeiros, ; Diagnostic Innovations in Glaucoma Study (DIGS): Relationship between Disease Severity and Reproducibility of Estimated Number of Retinal Ganglion Cells in Glaucoma. Invest. Ophthalmol. Vis. Sci. 2013;54(15):2251.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the influence of disease severity on the reproducibility of estimates of retinal ganglion cell (RGC) counts in a cohort of stable glaucoma patients.
This study included 55 eyes of 29 glaucoma patients followed for 5 weeks. Subjects were recruited from the Diagnostic Innovations in Glaucoma Study (DIGS). All eyes underwent weekly retinal nerve fiber layer (RNFL) imaging with Spectralis spectral domain optical coherence tomography (SDOCT) and visual field testing with standard automated perimetry (SAP). Estimates of RGC count were obtained from SAP (SAP-RGC) and SDOCT (SDOCT-RGC), and a weighted average (WRGC) was used to obtain a final estimate of the number of RGCs for each eye using structural and functional data. It was assumed that during the 5 weeks of follow-up the disease did not progress and that any change in measurements with retesting represented variability. Absolute differences between baseline and each follow-up were calculated. Intra-class correlation coefficients (ICCs) and weighted least squares (WLS) linear regression analysis were used to evaluate the influence of disease severity, measured by average Mean Deviation (MD), on the reproducibility of RGC count estimates.
The average number of visits per patient was 4.4±0.9. The average MD was -5.07±6.86 dB, ranging from -25.21 to 1.55 dB. The apparently high reproducibility of SAP MD (in dB) in early disease corresponded actually to a large variability when the same data was translated into number of RGCs (SAP-RGC). Both WRGC and SAP-RGC had less variability with worse disease severity; however, WRGC had less variability than SAP-RGC in the entire disease spectrum (Figure). The ICC for the combined structure and function estimate of RGC counts was 0.99, indicating high reproducibility.
Visual field testing, when assessed in terms of RGC counts, shows higher variability in early compared to advanced stages of disease. WRGC, a new index representing a combined structure-function estimate of RGC counts, provides more consistent reproducibility across the spectrum of disease and shows promise for improving our ability to assess glaucomatous progression.
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