Symptoms

The cones are not only important for color vision, but especially for sharp vision, since the retina contains only cones at the point of sharpest vision, the yellow spot, with which we usually fixate points. The rods do not offer by far the same resolution as the cones, but they are more sensitive to light, which is why they are used in healthy people, especially in twilight vision. These properties result in the four main symptoms of color blindness: First, of course, the lack of the ability to perceive colors.

For those affected, however, it is much more serious that their visual acuity (visual acuity) is significantly reduced. In addition, one finds fast, twitching eye movements (called nystagmus), which are due to the missing cones in the yellow spot: The body tries to find other fixation points than the yellow spot by the fast movements and thus compensate for the reduced visual acuity. The last important symptom is the increased sensitivity to glare, which leads to photophobia and is caused by the fact that only the highly light-sensitive rods absorb light stimuli. As a result, patients can hardly see anything in the light; for this reason, color blindness is sometimes colloquially referred to as “day blindness”.

Diagnosis

In the congenital form of color blindness, it is possible to use blood analysis to examine the genes responsible for the disease and to detect mutations. It is also possible to perform a so-called electroretinogram (ERG), in which light stimuli are presented to the person being examined, whose effect on the brain is then recorded with the aid of electrodes. During interpretation, the activities of cones and those of rods can be assessed separately.

Therapy of color blindness

Frequently used tests for color blindness are the Ishihara or Stilling-Velhagen color charts, which do not recognize numbers or letter patterns of patients with color vision disorders. The patterns have different color saturation, but the brightness value is identical to the background. So the recognition is independent of contrast differences.

In addition, there is the Farnsworth test in which 16 color slices are to be sorted according to color gradation. It starts with a dark blue tone. Color-blind people tend to typical mix-ups within the series. Another possibility to determine color blindness is the anomaloscope where the color blind are supposed to create a certain yellow tone by superimposing red and green tones. People who have difficulty recognizing red tones mix in too much red, green-blind people too much green.