An Unheard Facts of Anomaloscope Color Blindness Test
This test will see if you can adjust the brightness of two lights. You will be looking through an eyepiece at 2 lights that have different levels of brightness. You will use knobs to adjust the lights and try to adjust them.
If you cannot reach the brightness of the 2 lights, you may be suffering from color blindness. An anomaloscope is a color vision instrument and color blind test commonly used to quantify and characterize color blindness.
They are expensive and require special skills to operate, but are considered the gold standard for color vision standards. As a result, they tend to be used for academic study rather than job hunting.
They are also used to validate other color perception standards related to the classification of color vision disorders.
Principle
An anomaloscope requires a subject to make a color match between a mixture color and a test color. The test color is a single spectral color, for which the subject can adjust the brightness. The mixture color combines two spectral colors, for which the subject can adjust the proportion, thereby changing the hue.
These two colored lights are positioned side-by-side and the subject changes the two parameters until the colors appear to match. The parameter values at match define the type and strength of the color vision defect.
The wavelengths of the three lights used for an anomaloscope are defined by the match of equation that the anomaloscope is defined to. There are four different matches:
Rayleigh Match — a test light at 589 nm (yellow) and mixture lights at 545 nm (yellow-green) and 670 nm (red). This is used to characterize red-green deficiencies.
Engelking-Trendelenburg Match — a test light at 490 nm (cyan) and mixture lights at 470 nm (blue) and 517 nm (green). This is used to characterize blue-yellow deficiencies.
Pickford-Lakowski Match — a test light from a tungsten bulb and mixture lights at 470 nm (blue) and 585 nm (yellow-orange) lights. This is used to characterize blue-yellow deficiencies.
Moreland Match — mixture lights at 436 nm (blue) and 490 nm (cyan) light. Unlike the other matches, the test light is not a monochromatic light where the brightness is adjusted. Rather, it is a dichromatic mixture of 480 nm (cyan-blue) light and its Complementary color 580 nm (yellow).
The yellow acts to desaturate the cyan-blue without changing its hue. The colors are therefore called the primary mixture color and the desaturant mixture color. This is used to characterize blue-yellow deficiencies.
RGB Anomaloscope Color Blindness Test
The anomaloscope is the most accurate tool to classify your color blindness. Since it was developed by a German ophthalmologist just over 100 years ago it is used all over the world to check the severity of ones color vision deficiency and its specific subtype.
The classical anomaloscope is used to identify red-green color blindness. It consists of two different light sources which have to be matched. One source is a yellow lamp which can be adjusted in its brightness.
The other one is made by a mixture of a red and a green lamp, whereas the mixture between those two colors can be calibrated.
- Red- vs. green-blindness,
- dichromacy vs. anomalous trichromacy,
- and the severity of your color vision deficiency,
As this tool is only available as a quite expensive equipment I tried to simulate it online. I knew that there is only a little chance to get the same results as the real anomaloscope.
But I tried it anyway and designed the RGB Anomaloscope. As all computer displays are based on the colors red, green, and blue, it will always be a simple approximation of the real test.
The diagram below shows the test results as matching-lines of some red-green colorblind persons.
Each point means that this person matched a certain red-green combination to some shade of yellow. Non-colorblind people would only match the point 50/50 with some variances.
According to the match the tool can tell you details about the following facts of your color blindness:
Unfortunately the results didn’t turn out as I thought. I couldn’t find any split between red- and green-blind persons. Also it isn’t that easy to judge the severity of a red-green color blindness.
A Severity Upgrade on RGB Anomaloscope Color Blindness Test
The diagram is now split into several colored areas. As your personal matching line starts growing from the center it is possible to find the severity of your red-green color blindness.
A very short line in the center means you are not colorblind, compared to a line stretching along the whole diagram which means you are suffering from a strong color blindness.
This update was based on more than 1’000 color blindness tests taken so far. I hope this helps you to find out more about your color vision.
I also checked the resulting matching points and found some interesting facts. The diagram to the side shows the colors which were matched with red.
The interesting fact is, that there are two main areas which can be identified. This points towards a possible differentiation of red- and green-blindness.
A Review on Anomaloscopy
Although the most common procedure for testing red-green colour deficiencies involves Ishihara plate and pseudo-isochromatic plates, other methods such as the use of anomaloscopes require skilled examiners and properly calibrated devices.
The advantage of using computer-based approaches to test colour vision is that the automation reduces the effect of natural bias of the examiner on the results, which leads to improved reliability of results. Digital storage of data also facilitates subsequent analysis and research.
The anomaloscope evaluates an individual’s Rayleigh matches, which are proportions of red and green light that need to be mixed to match the yellow light used as the test stimulus.
This procedure tests for red-green deficiencies. A vertically orientated bi-field composed of the top half (a mixture of red and green lights) and the bottom half (yellow light) is presented to a patient.
The proportion of red and green lights in the mixture and the intensity of the yellow light are adjustable, and the patient is asked to control both the top and the bottom fields until a match is obtained.
A NT observer will accept a narrow range of matches. With a scale of 0 being pure green and being pure red, the NT will produce a result of around 42 units.
A protanomalous observer will need more red in the mixture whereas a deuteranomalous trichomat will need more green in the mixture to match to yellow.
A dichromat will be able to match the yellow to pure red, pure green and all mixtures in between by adjusting its intensity, whereas a protan observer will need to turn down the intensity of the yellow light when matching the field to the red one, owing to their reduced sensitivity to red light.
Definite diagnosis of protanopia, protanomaly, deuteranopia and deuteranomaly can be diagnosed using anomaloscopy. A Pickford-Nicholson anomaloscope was simulated using a cathode ray tube (CRT) monitor, and this computer screening system was tested by comparing its diagnoses with diagnoses yielded by another colour vision test (Ishihara plates).
The sensitivity of the computer test was equal to that produced by the Ishihara plate test, supporting its use as a screening test for observers with anomalous chromatic vision.
Can Online Anomaloscope Differentiate Red-Green Color Blindness?
The RGB Anomaloscope can be used to check if you are suffering from red-green color blindness or not. Unfortunately it is not possible to differentiate between the different forms of red-green color vision deficiency.
Our online anomaloscope is based on matches between yellow and a mixture of red and green — like the real anomaloscope. The matches you make can tell you, if you are suffering from red-green color blindness or not (because if you are not colorblind, you can’t make any matches).
In an earlier update of the anomaloscope (Severity Upgrade), I found an interesting looking pattern in the matching colors. We had two peaks which looked like a pattern for differentiating between red- and green-blindness.
- Red-blindness shifts the peak of red sensitive cones towards the peak of the green ones. Because of that you have problems in differentiating certain colors and also your red starts looking much darker.
- Green-blindness works the other way around. The peak of the green sensitive cones is shifted towards the red peak. This causes a very similar form of color blindness, but in contrast to red-blindness, red doesn’t start to look darker.
This diagram shows the number of people taking the test, which declared to be green-blind and matched a certain yellow value (horizontal axis) to either green (#00FE00) or red (#FF8000).
The above diagram can’t tell us anything about a pattern. We have to compare it to the diagram, which is based on the numbers from people who declared to be red-blind.
The vertical axis has been adjusted in this diagram, as there were more people who declared to be red-blind. So the two diagrams can be compared 1 : 1.
