Thursday, October 28

When colors are not well perceived

Red like tomato, green like grass or blue like the sea. We usually associate colors with everyday images to describe them. Something that is simple for most people but that is not so easy for others who have trouble distinguishing some of these colors.

When we observe an object, nerve impulses reach the brain that originate from photoreceptors in the retina.

What the human eye does is compose colors from the combination of the three basic ones: the red, blue and green, associated with different types of cones, which are cells in the retina that help us perceive colors. Each type of cone has a different range of sensitivity to light, with a different photopigment: one sensitive to red light, another to green light, and a third to blue light.

Under normal conditions, when the combination of these three basic colors works correctly, we can perceive about 8,000 colors and shades. For example, the perception of yellow is the result of a combination of green and red cone inputs and little blue input. The target is perceived from the stimulation of the three cones.

This normal functioning of color perception is what is known as trichromacy. But what happens when this combination of cones is disturbed? Are the colors perceived the same?

When the colors are not well distinguished

The reason why colors are not distinguished well is a failure of the genes that are responsible for producing the pigments of the cones. Hence, as the American Academy of Ophthalmology admits (AAO), most people who have this problem are born with it (congenital condition).

This would also explain why it is a problem that usually affects men more (a 8% versus 0.5% of women) since the genes that encode the pigments of the green and red cones are found on the X chromosome, present twice in females (XX) and once in males (XY).

Although it can also happen that the problem is due to a pathology of the optic nerve, degenerative alterations of the retina or cataracts.

With this congenital condition, you may have one of three types of color perception disturbances: deuteranopia, due to affectation of the cones sensitive to green; protanopia, due to affectation of the cones sensitive to red; or tritanopia, which makes it difficult to perceive the color found on the blue-yellow axis; dichromaty, for which a type of color is not well distinguished, explains Dr. Francisco Javier González García, specialist of the Ophthalmology Service of the Rey Juan Carlos de Móstoles Hospital and responsible for the blog In a blink of an eye.

A problem that cannot be cured

These deficiencies in color vision, although they have some solutions in the form of ophthalmic lenses with a color filter, do not yet have any type of medical or surgical treatment.

It cannot be cured, which is why in children it can cause learning problems and in adults difficulty in performing from different work tasks (some professions evaluate these capacities in a specific way) to other everyday or mundane ones, such as recognizing the ripe fruit of those who do not. it is.

Finding out that you have this genetic alteration can make dealing with them in everyday life easier because most people use a variety of strategies to compensate for this difficulty and find ways to adjust.

There are also some tools that help, such as the Health advice guide on Occupational Road Safety, which gives some tips to drivers with contrast sensitivity disorders.

What are the visual tests that detect these alterations

Knowing if we have this problem is relatively easy. The most common tests to detect an alteration in color vision are two: Ishihara pseudoisochromatic plates and the Farnsworth-Munsell color ordering test. The first, developed about 100 years ago, is still one of the tests par excellence to detect problems with the colors red and green.

It consists of a series of background circles with dots of different colors and sizes. Some of these points form numbers or figures. If we have a problem with red and green, these figures or numbers will be difficult to see (we may not even see them at all).

The Farnsworth-Munsell Color Ordering Test uses blocks of different shades of the same color. The original test consists of 85 color cards separated into 4 ranges. The person has to place the cards in chromatic order between the reference cards.

One of the main advantages of this test is its ability to detect small, even minor, defects. The downside is that it is a very slow test to perform and very demanding for the patient (it is not recommended for children under 10 years of age).



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