Automated visual assessment system with steady state visual evoked potential stimulator and product detector

• US 4,861,154 A
• Filed: 08/06/1986
• Issued: 08/29/1989
• Est. Priority Date: 08/06/1986
• Status: Expired due to Fees

• Current Assignee: Northrop Grumman Corporation
• Original Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Inventors: Schmidt, Albert L., Hanes, Lewis F., Sherwin, Gary W.
• Primary Examiner(s): Bovernick, Rodney B.
• Assistant Examiner(s): Ryan, Jay Patrick
• Application Number:
  US06/893,758
• Time in Patent Office: 1,119 Days
• Field of Search: 351/211, 351/205, 351/222, 351/223, 351/237, 351/239, 128/731, 128/745
• US Class Current: 351/205
• CPC Class Codes: A61B 3/02 Subjective types, i.e. testing apparatus requiring the active assistance of the patient
• CPC Class Codes: A61B 3/0325 provided with red and green targets
• CPC Class Codes: A61B 5/377 using evoked responses
• CPC Class Codes: A61B 5/398 Electrooculography [EOG], e.g. detecting nystagmus; Electroretinography [ERG]

Abstract

An automated visual testing system is disclosed which presents an alternating steady state visual stimulus to a patient through an optical system that modifies the stimulus image. As the image changes, the patient produces evoked potentials that change. The evoked potentials are detected by a product detector which produces the amplitude of the evoked potentials. The amplitude is monitored through an analog to digital converter by a supervisor computer. The supervisor computer produces patient response curves from which it diagnoses visual system malfunction and/or prescribes correction. A control processor controls a stimulus generator to produce the image and an optical system, that includes polarizers, an astigmatism test slit or a cylindrical lense, a zoom lense system and a variable focal length test lense, transmits the image to the patient. The steady state visual potential stimulus generator is a device by which a rapidly complementing or flashing pattern can be presented to the patient. The generator allows the contrast of the image to be varied without varying luminance and allows operation in a true bicolor and multicolor mode. The product detector detects the level of the steady state evoked potential signals even in the presence of substantial background noise and extraneous electroencephalographic signals. These detectors can be used to monitor the evoked potential produced by visual, all or somatic steady state stimuli. The components described above can be used to produce a system that can determine to which of several different displays an observer is paying attention by providing images that blink at different frequencies and product detectors for each of the stimulus frequencies. The product detector producing the highest output indicates the display upon which the observer is focused.

Claims

1. A visual testing apparatus, comprising:

control means for stimulating the visual system of a patient with a test image at a stimulus frequency during a selected one of refractometry, acuity, astigmatism, contrast and color vision tests;

said control means comprising;

a control processor;

a mirror stimulus generator connected to and controlled by said control processor to produce an alternating stimulus pattern image; and

a lens system between the patient and said mirror stimulus generator, and connected to and controlled by said control processor, said lens system including eye drift prevention means for preventing the patient'"'"'s eye from adapting to a changing stimulus;

sensing means for detecting evoked potentials produced by the test image in the patient'"'"'s brain at the stimulus frequency during the selected test; and

analysis means for analyzing the evoked potentials produced by the patient during the selected test and displaying the results of the selected test.

2. An apparatus as recited in claim 1, wherein said image is polarized and said lense system includes:

a rotatable polarizer through which the test image passes;

a selectable slit through which the test image passes;

a zoom lense through which the test image passes; and

a variable focus test lense through which the test image passes.

3. An apparatus as recited in claim 1, wherein said lense system includes:

a zoom lense through which the test image passes;

a variable focus cylindrical lense through which the test image passes; and

a variable focus test lense through which the test image passes.

4. An apparatus as recited in claim 1, wherein said drift prevention means comprises:

a television and far field lense producing a reference image; and

a beam combiner that combines the test image and the reference image.

5. A visual testing apparatus, comprising:

control means for stimulating the visual system of patient with a test image at a stimulus frequency during a selected one of refractometry, acuity, astigmatism, contrast and color vision tests;

sensing means for detecting evoked potentials produced by the test image in the patient'"'"'s brain at the stimulus frequency during the selected test, said sensing means comprising;

self-preparing electrodes attachable to the patient'"'"'s head for detecting evoked potentials; and

a product detector, operatively connected to said electrodes and said analysis means, for detecting the amplitude of the evoked potentials at the stimulus frequency; and

analysis means for analyzing the evoked potentials produced by the patient during the selected test and displaying the results of the selected test.

6. A visual testing apparatus, comprising:

control means for stimulating the visual system of a patient with a test image at a stimulus frequency during a selected one of refractometry, acuity, astigmatism, contrast and color vision tests;

sensing means for detecting evoked potentials produced by the test image in the patient'"'"'s brain at the stimulus frequency during the selected test, said sensing means comprising;

self-preparing electrodes attachable to the patient'"'"'s head for detecting evoked potentials; and

a product detector, operatively connected to said electrodes, for detecting the amplitude of the evoked potentials at the stimulus frequency;

analysis means for analyzing the evoked potentials produced by the patient during the selected test and displaying the results of the selected test; and

a reference product detector for detecting brain wave activity at a frequency other than the stimulus frequency, the amplitude detected by said product detector is adjusted by aid analysis means using the brain wave activity detected by said reference product detector.

7. A visual testing apparatus, comprising:

control means for stimulating the visual system of a patient with a test image at a stimulus frequency during a selected one of refractometry, acuity, astigmatism, contrast and color vision tests;

sensing means for detecting evoked potentials produced by the test image in the patient'"'"'s brain at the stimulus frequency during the selected test; and

analysis means for analyzing the evoked potentials produce by the patient during the selected test and displaying the results of the selected test, said analysis means comprising a computer that filters the evoked potentials, produces result curves, and produces results values based on the result curves.

8. A stimulus generator for a patient, comprising:

first and second light sources each having red, green and blue lights and each source capable of producing a continuously variable colored light mixture; and

a patterned mirror, the first light source producing light that passes through the mirror to the patient, the second light source producing light reflected off the mirror to the patient.

9. A stimulus generator for a patient, comprising:

first and second light sources each having red, green and blue light sources;

a patterned mirror, the first light source producing light that passes through the mirror to the patient, the second light source producing light reflected off the mirror to the patient; and

light control means for changing activation times of the red, green and blue sources.

10. A generator as recited in claim 9 further comprising diffusion means for uniformly diffusing the light from said colored light sources over the mirror surface.

11. A stimulus generator for a patient, comprising:

first and second light sources;

a patterned mirror, the first light source producing light that passes through the mirror to the patient, the second light source producing light reflected off the mirror to the patient;

a third light source washing out light from the mirror, said first through third light sources producing continuous light;

first polarizing means for polarizing the light from the first and second sources in a first direction;

second polarizing means for polarizing the light from the third source in a second direction perpendicular to the first direction; and

a rotatable polarizer through which the light from the mirror and the third source pass.

12. An apparatus for determining a display to which an observer is paying attention, said apparatus comprising:

display means simultaneously producing images that flicker at different frequencies, the observer viewing said display means;

detection means, coupled to the observer by electrode means for contacting the observer'"'"'s head, for detecting the amplitude of evoked potentials produced in the observer'"'"'s brain at the different frequencies; and

comparison means, operatively connected to said detection means and including means for storing amplitudes, for determining which amplitude is the largest, the largest amplitude indicating which of said display means is receiving the greatest amount of attention.