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Felipe A. Medeiros, Linda M. Zangwill, Douglas R. Anderson, Christopher A. Girkin, Jeffrey M. Liebmann, Ronald S. Harwerth, Marie-Josée Fredette, Robert N. Weinreb; Estimating the Rate of Retinal Ganglion Cell Loss in Glaucoma with a Combination of Structural and Functional Tests. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2261.
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To present and evaluate a new method of estimating rates of retinal ganglion cell (RGC) loss in glaucoma by combining structural and functional measurements.
The study included 213 eyes of 213 glaucoma patients followed for an average of 4.5±0.8 years with annual standard automated perimetry (SAP) visual fields and optical coherence tomography (OCT) imaging of the retinal nerve fiber layer. A control group of 33 eyes of 33 glaucoma patients had repeated tests over a short period of time to test the specificity of the method. An additional group of 52 eyes from 52 healthy subjects followed for an average of 4.0±0.7 years was used to estimate age-related losses of RGCs. Estimates of RGC counts were obtained from SAP and OCT and a weighted average was used to obtain a final estimate of the number of RGCs for each eye. The rate of RGC loss was calculated for each eye using linear regression. Progression was defined by a statistically significant negative slope faster than the age-expected loss of RGCs. The number of eyes progressing based on rates of RGC loss was compared to the number progressing based on rates of SAP Visual Field Index (VFI) and OCT average thickness change.
From the 213 eyes, 47 (22.1%) showed statistically significant rates of RGC loss that were faster than the age-expected decline. The mean rate of RGC loss in these eyes was -33369 cells/year (range: -8332 cells/year to -80636 cells/year). 18 (8.5%) eyes showed significant rates of VFI loss and 31 (14.6%) eyes showed significant rates of OCT average thickness loss. A larger proportion of glaucomatous eyes showed progression based on rates of RGC loss than VFI or OCT average thickness (P<0.01 for both comparisons), while maintaining similar specificities in the stable group.
In conclusion, the rate of RGC loss estimated from combining structure and function performed better than either isolated structural or functional measures for detecting progressive glaucomatous damage. The use of such rates may improve detection of change in clinical practice and in trials evaluating disease progression.
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