Differential diagnosis of sensory abnormalities using a normalized, ratiometric analysis of steady state evoked potentials
First Claim
1. A machine implemented method for testing a visual sensory system of a vertebrate to obtain measurements for use in determining whether a disease condition exists and for differentiating disease affecting the linear pathway of the sensory system from disease affecting the non-linear pathway of the sensory system, the method comprising:
- (a) applying a periodic visual stimulus to the eye of the vertebrate;
(b) detecting the periodic electrical signal evoked by the stimulus in the brain of the vertebrate;
(c) detecting the amplitude of selected Fourier components of the evoked signal, said components being selected to enable the performance of step (d) and to exclude any higher order components at frequencies which are present in said periodic visual stimulus, one of said components being a first order factor;
(d) machine computing a ratio having a numerator and a denominator representing the ratio of the transfer functions of said linear and non-linear pathways, either the numerator or denominator including a first order amplitude factor selected and detected in step (c) and the other including a higher order amplitude factor selected and detected in step (c).
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Abstract
A method for testing the visual system to detect the presence of disease, and to distinguish disease which has degraded the linear visual pathway from disease degrading the nonlinear visual pathway in a manner which is substantially independent of the stimulus applied to the eye and the connection of the instrumentation to the patient being tested. Three light sources having their amplitude varied at different frequencies stimulate the eye. The response evoked in the brain is detected and Fourier analyzed. The amplitude of selected Fourier components are detected and used to compute a ratio which removes the dependence upon the factors stated above. The Fourier component amplitude factors are selected so that the number of factors in the numerator of the ratio is equal to the number in the denominator and the sum of the orders of the factors in the numerator are equal to the sum of the orders in the denominator. This provides a ration of the response of the linear system to the response of a nonlinear system, which can be compared to a data bank of such test results to determine whether a particular patient being tested deviates enough from the normal response to suspect disease, and the direction and magnitude of that deviation so that the type and extent of disease can be indicated.
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Citations
14 Claims
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1. A machine implemented method for testing a visual sensory system of a vertebrate to obtain measurements for use in determining whether a disease condition exists and for differentiating disease affecting the linear pathway of the sensory system from disease affecting the non-linear pathway of the sensory system, the method comprising:
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(a) applying a periodic visual stimulus to the eye of the vertebrate; (b) detecting the periodic electrical signal evoked by the stimulus in the brain of the vertebrate; (c) detecting the amplitude of selected Fourier components of the evoked signal, said components being selected to enable the performance of step (d) and to exclude any higher order components at frequencies which are present in said periodic visual stimulus, one of said components being a first order factor; (d) machine computing a ratio having a numerator and a denominator representing the ratio of the transfer functions of said linear and non-linear pathways, either the numerator or denominator including a first order amplitude factor selected and detected in step (c) and the other including a higher order amplitude factor selected and detected in step (c). - View Dependent Claims (3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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2. A method in accordance with claim 2 wherein the numerator and the denominator are each a product of a multiplication of selected Fourier component amplitude factors, the number of factors in the numerator being equal to the number of factors in the denominator so that output gain factors will be cancelled and the sum of the orders of the factors in the numerator being equal to the sum of the orders of the factors in the denominator so that input gain factors will be cancelled.
Specification