Rare eye diseases
Dyschromatopsia is a deficiency in the perception of colours. When an individual has a complete inability to recognise the chromatic scale, this is called achromatopsia.
There are two types of dyschromatopsia depending on the origin: congenital or hereditary and acquired. The term Daltonism refers to congenital dyschromatopsia.
The cells responsible for seeing colours (chromatic vision) are the retinal photoreceptors called cones. They are mainly located in the central portion named the macula. There are three types of cone depending on the colours they are able to perceive: red (with a wavelength of 549 to 570nm); green (522 to 539nm) and blue (114 to 424nm).
Congenital dyschromatopsias are classified depending on the colours they are capable of perceiving:
– Protanopia: The cones that perceive the colour red are missing.
– Tritanopia: The phoreceptors that code the colour blue are missing. It's the most uncommon.
– Deuteranopia: The absence of the ability of perceive the spectrum of the colour green.
– Protanomalies: Loss of red–green vision due to poor functioning of the cones sensitive to red.
– Deuteranomalies: Loss of green vision due to a shift in the functioning of the cones sensitive to green.
– Tritanomalies: Loss of the blue–green spectrum due to a shift in the cones that identify the colour blue.
The origin of dyschromatopsia may lie in a genetic or acquired disorder. Hereditary dyschromatopsia may be due to a change in the X chromosone. This leads to the disease being transmitted by the woman even though its the man who is suffering from the disorder.
The acquired causes for a certain degree of dyschromatopsia are multiple and varied. Within one same pathology there may be many types of shifts in the perception of colour without there being any shift specific to a determined entity. The most common are macula diseases (where there is a very high number of cells responsible for the perspetion of colour, the cones).
Within these, we must highlight, in particular, age-related macular degeneration, a pathology that changes the anatomy of the macula and, as a consequence, the cells located therein. Other pathologies may include ones of an infectious or toxic origin. Different anomalies like the formation of cataracts or changes to the optic nerve may give rise to a range of types of dyschromatopsias.
It is important to recognise the differences in symptomology between the congenital and acquired dyschromatopsias when it comes to performing a differential diagnosis. The acquired are usually asymmetrical, they are associated with functional shifts other than anomalous perception of colours and they usually affect the red-green and blue-yellow axes. The congenital, on the other hand, usually affect both eyes and are symmetrical, the rest of the visual functions remain intact, the shift usually becomes stable over time and most frequent error is red-green perception.
There is a range of specific chromatic vision tests.
We have highlighted the two most commonly used:
Frequently asked questions
A treatment does not currently exist as it is a genetic mutation that causes the symptoms.
From birth itself, as there is already a cell change of a genetic origin. In many cases, the symptomology is so mild that the patient cannot identify mistakes in their perception of colours until they undergo a specific chromatic vision test.