Achromatopsia (ACHM) is a rare color disorder in which the patient cannot perceive colors, but only contrasts (light-dark). It is to be associated with nystagmus, photophobia and severely reduced visual acuity.
For most patients, the complete form is present, which leads to a complete loss of function of all three types of cone cells. The incomplete ACHM is less common, with similar but less pronounced symptoms.
The pendulum nystagmus comes about because, in the "yellow spot", (place of the sharpest vision) only rod cells are active, and this defect should be compensated by rapid eye movements. The decrease in vision (usually only 10% of normal vision) results from the fact that the centrally located rod cells are present at a lower density than the cone cells, responsible for the daytime vision.
Since rod receptors are designed for smaller amounts of light (twilight vision / night vision) than those of the cones, a strong glare sensitivity additionally develops. The ACHM is inherited as an autosomal recessive trait.
Five different genes can currently be linked to the disease. They all encode components of the visual transduction cascade. Most commonly, mutations can be found on the CNGB3 gene and the CNGA3 gene. Women and men are equally affected.
There is no specific therapy. The low visual acuity can not be compensated by glasses. However, one or more of several special glasses (edge filters) or (tinted) contact lenses are necessary in any case to compensate for the high sensitivity to light.