Anomaloscope

Red-Green START Tritan (Blue) START


Contents


Online anomaloscope

The online anomaloscope is a very simple red-green color blindness test. Try to match 7 pairs of colors. You can get a match while using the slider. If you get an exact match, press ‘Match’ and if you can’t match them use the ‘No Match possible’! button.

This test is only a demonstration of the original anomaloscope. Its efficiency is not comparable with the original instrument. Anoaloscope uses 3 primary monochromatic colors (670 nm - red, 546 nm- green and 589 nm - yellow), while in the online version, the yellow is a mixture of red and green colors. As every color on a computer display is made up from the three base colors red, green, and blue, an anomaloscope can’t be reproduced online. So this is just a simple reproduction, due to the different operating principle.

The wider the range you are able to find match with the reference color, the more severe color blindness you have.

scale anomaloscope color blind test


Anomaloscope

anomaloscope color blind test

The first anomaloscope was developed in the 20th century and since then it is the most accurate color blindness test instrument used by eye specialists all around the world.

How it works

An anomaloscope is based on a color match. Two different light sources have to be matched to the same color. On one side you have a yellow color which can be adjusted in brightness. The other side consists of a red and a green light whereas the proportion of mixture is variable.

The anomaloscope allows evaluation of an individual’s Rayleigh matches, ie the proportions of red and green light that need to be mixed to match a yellow. The currently available Neitz OT and Oculus Heidelberg anomaloscopes are designed to perform in the same way as the original Nagel anomaloscope, which is no longer available.

The patient is presented with a bi-field, one half composed of a mixture of red and green lights, the other a yellow light. The proportion of red and green lights in the mixture and the intensity of the yellow light are adjustable. The patient can be asked to perform free matches, ie control both the top and the bottom field until a match is obtained. However, more commonly, the practitioner sets the red/green mixture and the patient will attempt to make a match by changing only the luminance of the yellow field.

anomaloscope diagnosis color blind test

Normal observer

An observer with normal color vision will accept only a narrow range of matches. With a scale of 0 (pure green) to 73 (pure red), the normal match will be around 42 units.

Anomalous trichromats

The anomalous trichromat will need a different proportion of red and green lights to match the yellow than the normal observer; the protanomalous observer will need more red in the mixture whereas the deuteranomalous trichromat will need more green

Dichromats

The dichromat will be able to match the yellow to a pure red, pure green and all mixtures in between by simply adjusting its intensity. Protan observers will turn down the intensity of the yellow light when matching the field to a red one. This is caused by their reduced sensitivity to red light.

A Rayleigh equation anomaloscope will therefore separate normals from color deficient observers, protans from deutans and anomalous trichromats from dichromats.

Most anomalous trichromats will show not only a shifted mid-point but also a greater range of accepted matches than individuals with normal colour vision. The extent of the matching range is an indicator of the severity of the defect, with a larger range reflecting a more severe defect.

anomaloscope diagnosis color blind test

Tritans

Attempts have been made to develop equations for the evaluation of tritan deficiencies, but these have been problematic, as the region within which the match has to be made is trichromatic, and is also subject to the effects of lens and macular pigments. The Oculus Heidelberg anomaloscope incorporates the Moreland equation: a mixture of blue and green lights to match a blue-green light.

BACK TO THE TESTS

Facebook Comments

Share on Myspace