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David F. Garway-Heath, Graham E. Holder, Fred W. Fitzke, Roger A. Hitchings; Relationship between Electrophysiological, Psychophysical, and Anatomical Measurements in Glaucoma. Invest. Ophthalmol. Vis. Sci. 2002;43(7):2213-2220.
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purpose. To evaluate the relationship between electrophysiological, psychophysical, and structural measurements in normal and glaucomatous eyes and to test the hypothesis that there is a continuous structure–function relationship between ganglion cell numbers and visual field sensitivity.
methods. Thirty-four normal subjects and 40 patients with glaucoma were examined with the pattern electroretinogram (PERG), perimetry and retinal tomography. Transient and steady state (SS) PERGs were recorded, and peak (P)-to-trough (N) amplitude was measured. The unit of differential light sensitivity (DLS) in perimetry is the decibel. The decibel is 10 · log(1/Lambert), where the Lambert is the unit of test spot intensity. PERG amplitudes were correlated with decibel and 1/Lambert DLS for the central 18° of the visual field and with neuroretinal rim area in the temporal part of the optic disc. Age-related changes in the structural and functional measurements were sought. The correlation between variables was investigated by linear and quadratic regression analysis. A quadratic (y = ax + bx 2 + c) fit was taken to be significantly better than a linear fit, if the coefficient (b) for the x 2 term was significant at P < 0.05.
results. A quadratic fit between decibel DLS and PERG amplitude (transient PERG: R 2 = 0.40, P = 0.0000; SS PERG: R 2 = 0.32, P = 0.0000) was significantly better than a linear fit. There was a linear correlation between 1/Lambert DLS and PERG amplitude (transient PERG: R 2 = 0.44, P = 0.0000; SS PERG: R 2 = 0.35, P = 0.0000). There was a linear correlation between temporal neuroretinal rim area and PERG amplitude (transient PERG: R 2 = 0.17, P = 0.0003; SS PERG: R 2 = 0.20, P = 0.0001). A quadratic fit between decibel DLS and temporal neuroretinal rim area (R 2 = 0.38, P = 0.0000) was significantly better than a linear fit. There was a linear correlation between 1/Lambert DLS and temporal neuroretinal rim area (R 2 = 0.30, P = 0.0000). Both DLS and PERG amplitude declined with age in the normal subjects. The rate of decline was −0.17%, −0.74%, −0.75%, and −0.78% per year for decibel DLS, 1/Lambert DLS, transient PERG, and SS PERG, respectively.
conclusions. There is a curvilinear relationship between decibel DLS and both PERG amplitude and neuroretinal rim area, and a linear relationship between 1/Lambert DLS and PERG amplitude and neuroretinal rim area. These findings support the hypothesis that there is no ganglion cell functional reserve but a continuous structure–function relationship, and that the impression of a functional reserve results from the logarithmic (decibel) scaling of the visual field.
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