Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Subjective type
Reexamination Certificate
2000-02-09
2001-04-03
Manuel, George (Department: 3737)
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
Subjective type
Reexamination Certificate
active
06210006
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a color discrimination vision test and more particularly to an apparatus and method which can be used to identify color vision deficiency and the degree of deficiency, if any, a test subject has.
Color discrimination testing is essential for many types of jobs where the ability of a person to recognize different colors is a fundamental part of a job. Color discrimination testing may also be used for diagnostic purposes to recognize medical conditions that may require attention. Prior art patents, including for instance U.S. Pat. No. 4,848,898 to Massof, describe in detail the human visual system and basic color deficiencies that may be discovered.
Several different tests are widely recognized and practiced. These tests include Ishihara plates, the Munsell-Farnsworth test, and Nagel's anomaloscope.
Ishihara's plates require the detection of numbers which are displayed in front of a background. The numbers and background are built up by spots varying in diameter and in hue. The hue of the spots is selected such as to cause confusion in color perception in color deficient people. Therefore, color deficient people are not able to group those spots together to form the number which is to be detected. Ishihara plates are used to detect red-green color deficiency. A short version of the test is used to determine color vision performance in a passed/failed manner for red or green color vision. The full test can additionally discriminate between “strong” and “weak” deficiency in color vision (two levels). Ishihara's test is very popular in clinical use as well as in the laboratory. Since the colors on the plate are produced by reflection of ambient light, the ambient light must have a specific spectrum (daylight) and must be of a give luminance (>500 lux) to ensure correct test conditions.
In the Farnsworth-Munsell test, 15, 65 or 100 filled circles (depending on the test) of varying hue are placed in random order on a table. The patient is asked to order the circles in a row so that neighboring circles differ as least as possible in color. The first color (hue=blue) in this row is fixed and given by the test. The Farnsworth-Munsell color test requires similar conditions for illumination as mentioned above for the Ishihara test. The interpretation of the results is somewhat more complicated than is the case for the Ishihara test. However, Farnsworth-Munsell enables an administrator to check for red-green as well as for blue yellow deficiency. Detection of degree of deficiency depends on one hand on the number of color circles used. An increasing number of circles goes in parallel with an increasing time needed to complete the test. For this reason, most administrators prefer to use the Farnsworth-Munsell version with 15 circles. On the other hand, the degree of deficiency can also be assessed (two levels) by using a desaturated version of the Farnsworth-Munsell test. However, this procedure sometimes makes the interpretation of results somewhat complicated (e.g. in the case where patients perform better in the desaturated test than in the standard test).
In the so called anomaloscopes (e.g. the Nagel anomaloscope), patients match the hue of two fields. One of the fields has a given hue. The complete anomaloscope test should be performed for different levels of luminance of the field with a fixed hue. The matching procedure consists in varying the luminance of two colors (in case of the red-green test, red and green) which are mixed and comparing the hue of the mixture to the hue of the field with a fixed hue.
Ishihara's test requires the test subjects to communicate the number detected. If the numbers are communicated verbally, the presence of a person is required to record the response. Recording of the information without a test administrator would require test subjects, e.g., to key in the number on a keyboard or a key pad. They therefore would have to change their fixation from the test plates to the keyboard. Beside ergonomical problems, the change of fixation will alter the state of a patient's visual system (e.g. change in level of adaptation) affecting therefore, the result of the test. Similar conditions are also true for the Farnsworth-Munsell and anomaloscope tests mentioned above.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to overcome the foregoing drawbacks and provide a color discrimination vision test method and apparatus that can be used to identify color vision deficiency and the degree of that deficiency, if any, of a test subject.
In one embodiment, the invention is a method of conducting a color discrimination vision test for a person. The method comprises several steps including displaying a test object comprised of two separate fields wherein one field has a fixed color hue and the other field has a variable color hue. The person being tested is then instructed to select which field corresponds to a color hue wherein one of the fields is the correct selection. The person's selection is recorded. Then, subsequent test objects are displayed that comprise the fixed color hue field and the variable color hue field wherein the variable color hue field is a color hue different from the color hue of the previous test object. The instructing and recording steps are then repeated. In a further embodiment, the color hue of the variable color hue field in the subsequent test objects is preselected to facilitate determination of how well a person discriminates between the fixed color hue and the variable color hue. Also, the fixed color hue can be yellow and the variable color hue can be green or red. Additionally, the variable color hue fields in the subsequent test objects are determined using a modified binary search technique. The subsequent test objects are displayed until there is a predetermined number of incorrect responses recorded or until there is a predetermined minimal difference in the color hues of the two fields. Preferably, the test is self administered without the need of an administrator being present.
In another embodiment, the invention is an apparatus for conducting a color discrimination vision test for a test subject. The apparatus comprises an image display adapted to display a plurality of test objects comprised of two separate fields wherein one field has a fixed color hue and the other field has a variable color hue. The apparatus includes a test subject input device and means for recording input from the test subject input device. The apparatus also includes means for controlling test objects displayed on the image display wherein the variable color hue field changes with the plurality of test objects displayed. In other embodiments, the test subject input device is adapted to be used blindly by a test subject. The test subject input device may also be a joystick.
REFERENCES:
patent: 4169285 (1979-09-01), Walker
patent: 4848898 (1989-07-01), Massof
patent: 5609159 (1997-03-01), Kandel et al.
Measuring Colour Vision Defects, portion of Web Page, www.geocites.com/Hot Springs/8018/Measure.html.
A Rapid Technique To Assess The Resting States Of The Eyes And Other Threshold Phenomena: The Modified Binary Search (MOBS), Tyrrell et al., Psychenomic Society, Inc., vol. 20(2), pp. 137-141, 1988.
36. TeaPP, Abstract-Band, Ludwig-Maximiliams-Universitat, Munchen.
Testing Color Perception with a PC, H. Krueger (with translation).
Manuel George
Millen White Zelano & Branigan P.C.
Titmus Optical, Inc.
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