Eye test: Colors on color charts
To test color vision, the doctor uses various color charts, for example so-called Velhagen charts or Ishihara color charts.
On the panels for the Ishihara test, there are pictures that are made up of dots in different colors, such as shades of red and green. Color vision patients can recognize objects such as numbers or figures through the different hues. If, on the other hand, a patient has color vision deficiencies, he or she cannot distinguish between the different hues and cannot recognize the contrasts. As a result, he either does not see individual figures at all or sees them incorrectly. The Velhagen color test is also based on this principle.
Ishihara and Velhagen eye test: Procedure
Red-green eye test and blue-green eye test run in the same way: First, the doctor presents the patient with the corresponding color vision charts at a reading distance of about 70 centimeters. He must also make sure that the patient has sufficient light to read the charts (natural daylight is best). Now the doctor asks the patient if he can recognize and correctly name the numbers or figures on the charts.
With the color vision test using the charts, the doctor can detect a color vision deficiency, but cannot determine exactly how pronounced it is.
Color vision test with the anomaloscope
A patient with red-green deficiency has a hard time with this task, because he always adds too much of the color he cannot perceive. In contrast to the color charts, this color vision test also allows a statement to be made about the severity of the color vision deficiency.
