What color is a leaf? We would all say green, but in reality this is not exactly the case because colors are the result of complex processes that start in our eyes and continue in the brain. Not only that: our mood can also affect the sensation of color. However, sometimes there may be alterations in the chromatic perception that give rise to real disorders such as dyschromatopsia, that is when the vision of colors is present but is altered. This disorder, better known as color blindness, leads to a poor perception of certain shades such as green or blue or red.
How color is born
To understand how we come to define the color of things, we have to go back to school when we were studying Isaac Newton and his experiments on horseback. The sun emits a light that appears white to us, but which is actually made up of all the colors of the rainbow mixed together. In his experiments in 1666, the English scientist had observed that, by passing a ray of sunlight through a crack and then hitting a triangular prism, it was decomposed into a fan, obtaining the so-called “chromatic stripe of the spectrum”: red, orange, yellow, green, blue, indigo and purple.
From the eye to the brain
Today we know that the process that leads to the formation of color is quite complex: “It begins in our eyes and continues in the brain with the processing of the information received at the level of the retina and then ends in the portion of the primary visual cortex, the occipital area” explains Luigi Mele, ophthalmologist surgeon, Luigi Vanvitelli University – Naples and President of the Scientific Committee of the Salmoiraghi & Viganò Foundation. What is perceived by the human eye as color are reflected radiation, because material bodies are neither luminous nor colored, but are perceived as such only by the human eye. “A black body – adds the ophthalmologist – absorbs all visible electromagnetic radiation, while a white body rejects them all. A normal eye is able to perceive not only the pure fundamental colors but also the various chromatic combinations that derive from the mixing of them performed in various proportions ”.
The psychology of color
Our mood, emotions and sensitivity also affect the way we perceive color. “In the field of visual perception – underlines Mele – colors arouse certain sensations. The fact that the taps have blue for cold water and red for hot water is not a random choice. In rescue systems, color contrasts often have a vitally important function: an orange dinghy on the blue of the sea has a very specific signaling character. The red in the traffic lights and in the warning signs indicates danger and almost automatically increases attention ”.
Disorders of color perception
Sometimes there are alterations that ‘spoil’ the perception of colors. One of these is achromatopsia which occurs when the subject has visual blindness in all three primary colors (red, blue, yellow). But the most frequent disorder is dyschromatopsia, better known as color blindness: it can be congenital when it is due to a recessive mutation on the X chromosome and is therefore linked to the sex of the individual ”, explains Mele. “Acquired dyschromatopsia, on the other hand, is often a symptom of eye diseases, lesions of the optic pathways and pathologies of the brain: it is not caused by genetic factors, but arises as a consequence of certain events that may be related to health or trauma”.
The causes of color disturbances
Are there any risk factors that predispose to this type of disorder? In fact, it has been seen that an altered chromatic sense can also occur in subjects suffering from macular degeneration, glaucoma, retinitis pigmentosa and optic neuropathies. “Defects in discriminating the different colors can derive from head trauma or stroke affecting the visual centers”, clarifies Mele who adds: “Among the various causes is the opacity of the lens, that is the cataract, which can lead to a albeit slight alteration of blue-yellow sensitivity. Furthermore, in alcoholics there is a reduction in color sensitivity, greater for blue-yellow than for red-green ”. Often even the use of sun lenses obtained with non-certified coloring processes causes an altered perception of color.
Other diseases that cause color deficiency
Those who are color blind can have a completely normal vision, but this disorder still has an impact because those who suffer from it cannot carry out some professions or all the activities that require the integrity of the chromatic sense. “There are also other diseases that can cause color deficiency,” Mele explains. They are diabetes, glaucoma, macular degeneration, Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, chronic alcoholism, leukemia and sickle cell anemia. Furthermore, subjects with an inadequate diet, especially those with vitamin A deficiency, have a general reduction in shade discrimination ”.
A ‘pit stop’ at the ophthalmologist
How to know if you suffer from a disorder of this kind? Statistically 8% of men and 0.5% of women are affected by an alteration of color vision. There are many chromatic evaluation tests that diagnose these alterations: “It is advisable to submit to these tests preschool children, those who make a first eye examination and all those who show problems in color perception”, suggests Mele. “The therapy involves the prescription of lenses with generic and / or specific filters that will act on the different wavelengths improving the perception of colors. In subjects with normal color perception and not color blind but with specific needs, such as sportspeople or particular categories of workers, the use of lenses with filters of certain colors increases sensitivity, tone and brightness “.