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L.M. Ayres, P. Lopez, R.C. Caruso; Estimation of the scotopic electroretinographic intensity–response function using an abbreviated protocol . Invest. Ophthalmol. Vis. Sci. 2004;45(13):5144.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The electroretinographic (ERG) b–wave intensity–response (I–R) function has been used extensively to analyze retinal function in patients with retinal disease. It provides more insights about retinal pathophysiology than does the "standard" scotopic ERG, in which only two stimulus intensities are used. The traditional approach for recording I–R functions involves the use of 10 or more stimulus intensities. This requires a considerable increase in testing time in comparison with that required for the standard ERG. The aim of this study was to determine if reliable I–R function estimates could be obtained using a small number of stimulus intensities. Methods: Twenty control subjects with normal ERG I–R function parameters, and twenty patients, in whom at least one of the function parameters was abnormal, were included in this study. ERGs were recorded following ISCEV recommendations after dark adaptation. The standard flash intensity of 1.64 cd.s.m–2 was attenuated from 4.0 to 0.0 log units in 0.2 log unit steps. I–R functions were calculated using either an extended protocol (all suprathreshold values) or an abbreviated protocol (the subset of values obtained with 3.2, 2.4, 1.6, 0.8 log units attenuation). The "second limb" was not used in the fit in either case. The usual Fulton–Rushton model (V = (Vmax . In )/ (In + kn)) was used to fit I–R functions, where Vmax is the plateau, k the semi–saturation constant, and n the slope. Results: The four data points used in the abbreviated protocol were sufficient to obtain a fit of the I–R function in all cases. The mean goodness of fit, assessed with the correlation coefficient, was 0.99 in both cases. Differences between the two methods were estimated using the Wilcoxon test. No significant differences were seen between the parameters obtained with the extended vs. the abbreviated protocol (mean Vmax: 341.54 vs. 345.03 µV, p = 0.677) (mean k: – 2.34 vs. – 2.30 log cd.s.m–2, p = 0.12) (mean n: 0.99 vs. 1.00, p = 0.294). The results were similar when the control group and the patient group were analyzed separately. Conclusion: While the use of a large number of data points, from b–wave threshold to plateau, remains the "gold standard" to obtain accurate I–R function parameters, a very reasonable estimate may be achieved using a limited number of well–chosen data points. With only a minimal increase in recording time in comparison with the standard ERG protocol, one can thus extract considerably more information about a patient's retinal function.
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