Tritanopia: the world in a changed color

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

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

Epidemiology

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

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

[ 2 ]

Causes tritanopias

Scientifically established causes of tritanopia, as with other types of color anomalies, are genetic disorders of color perception, which in this case are associated with the lack of sensitivity of the eye to waves of the blue spectrum of light radiation.

The retina of the eye, which perceives light, is formed by two types of photoreceptor cells – the so-called rods and cones. Color is perceived by 4.5-5 million cones in the central part of the retina (macula); three types of cones have been identified, conventionally designated as L (there are about 64% of them in the retina), M (about 32%) and S (approximately 3-4%).

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

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

This anomaly is characterized by either the absence of OPN1SW type S-cones in the retina, or their genetically determined dystrophy, or a pathological change in the structure of the iodopsin photopigment, which is sensitive to the blue spectrum of light.

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

[ 5 ], [ 6 ]

Risk factors

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

• with age - due to macular degeneration; [ 7 ]
• with the effect of ultraviolet radiation on the retina;
• with diabetes (in which diabetic retinopathy develops and the thickness of the retina in the macula area decreases); [ 8 ]
• with blunt trauma to the eye or traumatic brain injury to the occipital part of the head;
• with alcoholism;
• with migraine. [ 9 ]

[ 10 ], [ 11 ], [ 12 ]

Pathogenesis

The pathogenesis of this anomaly lies in a heterozygous mutation – a disruption of the amino acid sequence of the OPN1SW gene encoding “blue” iodopsin on chromosome 7q32.

Since tritanopia is not linked to the X chromosome, this color anomaly is equally likely to occur in both males and females.

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

Symptoms tritanopias

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

Thus, people with tritanopia see everything that is blue or green as grey, and confuse blue with green; they see violet and orange as red, brown as pinkish-lilac, yellow as pink, and dark purple as black.

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

Diagnostics tritanopias

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

The computer simulator of tritanopia, or more precisely, the simulator of color blindness or Color Blindness Simulator (simulator of color blindness) has no diagnostic purpose, but makes it possible to convert photographs in normal color (in raster jpeg format) into an image that people with tritanopia, as well as protanopia and deuteranopia, see.

There are also color blindness simulators called Spectrum for the Chrome web browser and Color Oracle for Windows, Mac, and Linux. Using these, you can see how your website looks to people with different types of color blindness, including tritanopia.

[ 18 ]

Differential diagnosis

The differential diagnosis of congenital tritanopia and dominantly inherited optic nerve atrophy is being carried out [ 19 ]