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- Rods without cones: a new effective test has been invented for those who see the world in gray
Rods without cones: a new effective test has been invented for those who see the world in gray
Russia has begun clinical testing of a new method for the early diagnosis of achromatopsia, a rare genetic disease in which a person sees the world in only shades of gray. The developed test makes it possible to distinguish this pathology from other causes of color perception disorders in children without complex and expensive studies, as well as to speed up diagnosis. On the International Day of Rare Diseases, February 28, Izvestia tells how many achromatopsia patients there are in our country and how a modern testing method can make their lives better.
Symptoms and prevalence of achromatopsia
Clinicians from Sechenov University and Burnazyan Federal Medical Center have begun clinical testing of a new method for the early diagnosis of achromatopsia, a rare disease in which a person sees the world as in a black-and-white photograph. If with color blindness a person sees colors, but confuses some of them, then with achromatopsia he sees the world in shades of gray, black and white, scientists told Izvestia. This is due to a malfunction of the cones, the retinal cells that are responsible for color perception. Their function is partially taken over by sticks, which provide the perception of light and shadow, as well as vision in low-light conditions. As a result, a person with achromatopsia can clearly distinguish the shape and contours of objects, but not the colors.
— For example, a rainbow will look like an arc of different shades of gray: the yellow zone looks light gray, the red zone dark gray, and some stripes may even merge, - explained Natella Sukhanova, ophthalmologist at the Sechenov Center for Motherhood and Childhood. — According to our research, most patients perceive red as the darkest or blackest, and blue as the lightest or even white (one of the patients could not see the blue circle on a white background, for him these colors were the same).
In addition, people with achromatopsia see better in semi-darkness than in bright light, which is also associated with increased activity of retinal rods, the specialist added.
The disorder is caused by "breakdowns" in the genes. The majority (80% of the patients who took the study) had mutations in the CNGB3 gene, while 20% had mutations in the CNGA3 gene. The disease is rare — there is about one patient per 30-40 thousand people in the world. Sometimes it occurs more often, which is explained by the "founder effect" — a new population is created by a small number of people, which is why a random mutation is transmitted to a larger number of children. For example, on the island of Pingelap (Federated States of Micronesia), the disease occurs in 5-10% of the population.
Achromatopsia significantly limits everyday life, starting with the little things — a person cannot determine the readiness of food by color or choose clothes that match each other. There are more serious difficulties, such as the inability to drive a car and choose certain professions. In addition to color perception disorders, patients often develop photophobia — it is difficult for them to be in the sun and look at a white screen. Visual acuity is usually reduced and can be up to 30%. The disease often affects the psychological state.
At the same time, achromatopsia does not progress and does not affect intelligence, unlike a number of other genetic ophthalmological diseases, Natella Sukhanova explained.
— Perhaps this is due to the fact that the brain is very plastic in childhood and, due to the lack of color vision, it trains to solve tasks familiar to other people in a non-trivial way, for example, to memorize the brightness of objects and their texture. Or maybe children with achromatopsia perceive the world in a different way, and this is not only due to color. All this has yet to be studied," the specialist said.
Scientists around the world are developing treatments for the disease, including through genetic engineering, but so far it is impossible to cure the disease. Nevertheless, it is possible to help the child adapt to his condition, the doctors noted. The ophthalmologist selects eyeglass lenses for the child with special light filters that protect the eyes from light and allow them to see the world more clearly.
How to diagnose achromatopsia
Scientists have developed a new specialized test based on their own research on the features of achromatopsia. It includes images that differ not only in color, but also in tone, saturation, and brightness. Now the method is being tested on the basis of the Sechenov Center for Motherhood and Childhood.
— The fact is that it can be difficult to distinguish achromatopsia from other ophthalmological ailments, such as optic nerve atrophy, due to the similarity of symptoms — poor eyesight, nystagmus (involuntary eye movement), cone dysfunction, — said Natella Sukhanova.
In order not to start treating a child for a non-existent disease, which "disguised" achromatopsia, and to help him adapt, it is important to make a diagnosis as early as possible. Conventional polychromatic tables (numbers or shapes drawn with circles of the same color against a background of circles of a different color), which help to identify color blindness, are powerless in achromatopsia: the patient either does not distinguish between images at all, or focuses on brightness rather than color.
To make a diagnosis, it is necessary to conduct genetic analysis, layer-by-layer retinal tomography and electrophysiological studies, however, such methods require the availability of specialized equipment and laboratory conditions, the scientists noted. Therefore, simpler and more accessible tests were needed to make a preliminary diagnosis before conducting expensive in-depth examinations.
Testing is carried out on a screen with a pre—calibrated color rendering - a spectrophotometer is used for this, which eliminates double-reading of the results. The subjects are asked to compare color images with gray ones of the same brightness. A person without achromatopsia can easily distinguish between blue and gray, even with the same brightness of the images. In contrast, it is difficult for a patient with this disease to distinguish a blue image against a light background.
The method is suitable for examining young children — from the moment when the child is able to describe what he saw. The new method makes it possible to distinguish achromatopsia from other visual impairments, assess the severity of the disease and determine the need for additional examinations.
— This is a really relevant development, and the test will be needed to distinguish achromatopsia from other causes of poor eyesight in a child faster and easier. This will help children and families, because early recognition will remove years of uncertainty and allow them to build a life based on photophobia and low visual acuity. And also for doctors, since screening is cheaper and scaled up, which means there are fewer unnecessary examinations," Andrey Demchinsky, Neuronet market expert and Director of Science at Elvis Neuroimplants, told Izvestia.
At the moment, it is known that achromatopsia occurs with a frequency of 1 per 30 thousand people, and there are about 5 thousand such patients in Russia, Anna Klyueva, ophthalmologist at the Centerplus clinic of the Central Research Institute of Epidemiology of Rospotrebnadzor, told Izvestia.
— The purpose of this technique is to confirm the diagnosis and exclude other variants that may produce similar symptoms (partial optic atrophy, Leber's amaurosis, ocular albinism), which narrows down the spectrum of genetic research and helps to choose the right treatment and rehabilitation tactics at the place of residence. It also allows you to correctly and, most importantly, quickly route the patient to receive genetically engineered therapy, which in most cases is the only treatment for such patients," the specialist noted.
In addition, the new approach makes it possible to include patients in follow-up and research earlier, which is especially important if effective gene therapy methods become available, the expert noted.
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