Anomaloscopy is a procedure used to diagnose and evaluate color vision deficiencies in ophthalmology (eye care). The examination focuses on the diagnosis of red-green deficiencies, which must be verified especially for the safe practice of some professions. These include, for example, pilots or bus drivers, as there is a particular risk in road traffic or air traffic. For this reason, the anomaloscopic examination is part of the medical fitness examination.
The color vision disorders are divided into different clinical pictures. Achromatopsia, this is a rare inherited disorder, in which no or only partial colors are perceived, but only contrasts (light-dark) or achromasia (color blindness), in which there is no perception of colors and the patients only recognize differences in brightness. Congenital color vision deficiencies include anomalous trichromasia which denotes (color deficiency for red, green and blue) and partial color blindness (dichromasia – two false colors each; monochromasia – false color is either red, green or blue). Dichromasia typically results in color confusion, and color vision deficiencies can also be acquired. Anomaloscopy is used to distinguish monochromatic red deficiency/blindness from green deficiency/blindness. The conceptualizations of color vision deficiencies are as follows:
- Protanomaly (red deficiency).
- Protanopia (red blindness)
- Deuteranomaly (green deficiency)
- Deuteranopia (green blindness)
- Tritanomaly (blueness)
- Tritanopia (blue blindness)
Indications (areas of application)
- Patients with suspected partial color blindness (red or green).
- The medical fitness examination for certain professions (e.g., pilots).
The procedure
Both protanomaly and deuteranomaly are based on a gene mutation in the retinal cones (color sensory cells of the retina), which lead to a disruption in the synthesis of the red and green visual pigment, respectively. As a consequence, only the remaining visual pigments are active in each case, resulting in partial color blindness.
Anomaloscopy is based on the concept of additive color mixing, which determines color perception in the human eye: As primary colors, red, green and blue result in the color white in human perception. When green and red color receptors are stimulated simultaneously, the color yellow is produced in the visual center of the central nervous system (brain).
During anomaloscopic examination, the patient looks through the device at a circle, one half of which projects a spectral yellow with the wavelength of 589 nm. The other half consists of a mixture of spectral red (671 nm) and spectral green (546 nm). This mixture also appears yellow. Now the subject is instructed to correct the color mixture (red and green) so that the half of the circle exactly matches the hue of spectral yellow. A patient with a red deficiency will add more red, and a green deficient patient will add more green to adjust the color perception. The mixing ratio is now used to determine the anomaly quotient, which provides a quantitative assessment of the degree of color deficiency:
- Normal – 0.7-1.4
- Protanomal (weak red) – 0.02-0.6
- Deuteranomal (green-weak) – 2.0-20.0
Anomaloscopy is a simple and effective procedure for distinguishing and quantifying red and green deficiency or blindness. It is regularly used in fitness-for-duty examinations.