Tritanopia: the world in a changed color

Among several types of human color vision anomalies, ophthalmologists differ in tritanopia, which is also called blue-yellow color blindness or tritanopic dichromasia.

What it is? This is the inability to distinguish blue color.

Epidemiology

According to statistics, tritanopia is observed in approximately 0.008% of men and women, that is, this is a rare anomaly. [1]

In other sources, the number of people with this defect is determined at the level of 0.01% or even 1%.

[2]

Causes of the tritanopia

The scientifically established causes of tritanopia, like those of other varieties of  color anomalies, consist in genetic disorders of color perception, which in this case are associated with a lack of sensitivity to the eyes to the waves of the blue spectrum of light emission.

The retina of the eyes, which perceives light, is formed by two types of photoreceptor cells - the so-called rods and cones. Color perceive 4.5-5 million cones of the central part of the retina (macula); Cones of three types were identified, conventionally referred to as L (about 64% of them in the retina), M (about 32%) and S (about 3-4%).

Due to the light-absorbing pigments - photopsins, which are transmembrane proteins and are located on the disks of cone membranes, differentiation of the waves of red (max length - 560-575 nm), green (max 530-535 nm) and blue (max 420-440 nm) spectra occurs. Read more -  Color vision.

Tritanopia is associated with defects of S-cones, which are responsible for the perception of short waves corresponding to the blue color, and the transmission of the bioelectric signal through the optic nerve into the cerebral cortex - a cascade of phototransduction.

With this anomaly, either the absence of the OPN1SW type S-flasks in the retina, or their genetically determined dystrophy, or a pathological change in the structure of the photopigment of iodopsin sensitive to the blue light spectrum is noted.

Tritanopia is associated with two amino acid substitutions in the blue sensitive opsin and is associated with such genes  BCP, BOP, CBT, OPN1SW [3], [4]

[5], [6]

Risk factors

Experts say that tritanopiya can be not only hereditary, but also acquired. And risk factors for its development are related:

• with age, due to macular degeneration; [7]
• with ultraviolet exposure on the retina;
• with diabetes (in which diabetic retinopathy develops and retinal thickness decreases in the area of the macula); [8]
• with blunt trauma of the eye or head trauma to the head;
• with alcoholism;
• with migraine. [9]

[10], [11], [12]

Pathogenesis

The pathogenesis of this anomaly lies in a heterozygous mutation, a violation of the amino acid sequence of the coding blue iodopsin of the OPN1SW gene on chromosome 7q32.

Since tritanopia is not associated with the X chromosome, this color anomaly is equally possible in both men and women.

[13], [14], [15], [16]

Symptoms of the tritanopia

The main symptoms of this incurable anomaly are the difficulties of distinguishing between all shades of blue, yellow and green, as well as orange, pink, purple and brown.

So, everything that has a blue or green color, people with tritanopia see gray, and blue is confused with green; purple and orange it seems to red, brown - pink-lilac, yellow - pink, dark-purple - black.

Classical (or acquired) tritanopia does not differ in its manifestations from congenital tritanopia; in addition, tritanopia can be considered as a reduced form of normal trichromatism. [17]

Diagnostics of the tritanopia

Ophthalmologists conduct a test for tritanopia, as well as diagnose all color anomalies, using special Rabkin tables (the Ishihara color test is similar abroad). Details in the material -  Check color perception and color perception.

The computer simulator tritanopii, more precisely, the simulator of color blindness or the Color Blindness Simulator (simulator of color blindness) does not have a diagnostic purpose, but it makes it possible to translate photos in normal color (in raster jpeg format) into an image that people see with tritanopia, as well as protanopia and deuteranopia.

In addition, there are Spectrum colorblind simulators for the Chrome web browser and Color Oracle - for Windows, Mac and Linux. Using them allows you to see what your website looks like for people with different types of color blindness, including tritanopia.

[18]

Differential diagnosis

Porvoditsya differential diagnosis of congenital acyanopsia and dominant hereditary optic nerve atrophy [19]