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Abstract #3492 Published in IGR 4-2
Relationship between electrophysiological, psychophysical, and anatomical measurements in glaucoma
Garway Heath DF; Holder GE; Fitzke FW; Hitchings RAInvestigative Ophthalmology and Visual Science 2002; 43: 2213-2220
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 + bx2 + c) fit was taken to be significantly better than a linear fit, if the coefficient (b) for the x2 term was significant at p < 0.05. RESULTS: A quadratic fit between decibel DLS and PERG amplitude (transient PERG: r2 = 0.40, p = 0.0000; SS PERG: r2 = 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: r2 = 0.44, p = 0.0000; SS PERG: r2 = 0.35, p = 0.0000). There was a linear correlation between temporal neuroretinal rim area and PERG amplitude (transient PERG: r2 = 0.17, p = 0.0003; SS PERG: r2 = 0.20, p = 0.0001). A quadratic fit between decibel DLS and temporal neuroretinal rim area (r2 = 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 (r2 = 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.
Dr. D.F. Garway Heath, Glaucoma Research Unit, Moorfields Eye Hospital, City Road, London EC1V 2PD, UK. david.garway-heath@moorfields.nhs.uk
Classification:
6.6.2 Automated (Part of: 6 Clinical examination methods > 6.6 Visual field examination and other visual function tests)
6.6.3 Special methods (e.g. color, contrast, SWAP etc.) (Part of: 6 Clinical examination methods > 6.6 Visual field examination and other visual function tests)
6.7 Electro-ophthalmodiagnosis (Part of: 6 Clinical examination methods)
6.9.1 Laser scanning (Part of: 6 Clinical examination methods > 6.9 Computerized image analysis)
