Color blindness
| Classification according to ICD-10 | |
|---|---|
| H53.5 | Color vision disorders - color blindness |
| H54.0 or H54.2 | Blindness and visual impairment - blindness in both eyes (H54.0, visual acuity <0.05) - visual impairment in both eyes (H54.2, visual acuity> 0.05) |
| ICD-10 online (WHO version 2019) | |
The color blindness , achromatopsia or Achromasie is a rare, often inherited disorder of color perception , in which no color , but only contrasts (light-dark) can be perceived. In ocular (or congenital) achromatopsia , the visual disturbance is localized in the retina, i.e. in the eye . In the cerebral (or acquired) achromatopsia a neurological disorder of color perception is present.
The term color blindness is often misleading because red-green poor eyesight is colloquially referred to as color blindness. However, this disease is only a color ametropia (color anomaly), which occurs in around 5% of the population (mostly men). In the medical and expert field, there is usually no clear distinction between the disability achromatopsia and the functional impairment color ametropia . Both diseases are listed together under the same ICD diagnostic code 53.5 (color vision disorders), whereby achromatopsia is medically classified as a complete loss of color sense with resulting further relevant symptoms (poor visual acuity , extreme sensitivity to glare).
Clinical picture
There are three varieties of color blindness that arise in different ways:
- Hereditary total color blindness is an autosomal recessive hereditary disease of the retina . Women and men are equally affected. The affected people (approx. 1 / 100,000) can only differentiate between shades of gray and are also referred to as achromats, the cause is achromatopsia . They also suffer from poor visual acuity and hypersensitivity to bright light. There are around 3,000 people with achromatopsia in Germany.
- A disease similar to achromatopsia is the blue cone monochromatism, in which there is still greater residual vision in the blue area and which is inherited in an X-linked manner ( locus Xq28).
- Color blindness can also occur as cerebral achromatopsia , for example after a stroke , traumatic brain injury or other brain lesions. It is therefore an acquired color disorder . The cause does not lie in the eye as a sense organ itself, but in the disturbed processing of the sensory perception “color”. Visual acuity is normal, since the color sensory cells function normally and the edge detection and surface separation, which takes place in upstream brain areas, is intact.
Ocular (congenital) achromatopsia
Causes of Color Blindness
The color receptors ( cones ) in the retina of the eye enable the color perception of the environment. There are three types of these color receptors that receive and transmit color stimuli . With achromats none of these types of cones work, so they cannot recognize any colors.
This vision is also necessary for sharp color vision during the day, so photopic vision is not possible. Achromatic lenses only have rod receptors designed for scotopic vision . These light-dark receptors enable people with normal vision to see twilight because they are more sensitive to light than the color receptors. Achromats therefore suffer from extreme sensitivity to glare on bright days. In bright light, their rods are overloaded, which almost completely reduces poor eyesight.
Achromatic lenses only see a foggy white / gray. That is why the disease is also called day blindness. At the point of sharpest vision on the retina (yellow spot) there are only cones and no rods in healthy people. Achromats have no functioning sensory receptors in the center of the retina. The poor central visual acuity in achromatopsia results in nystagmus , an involuntary eye tremor that is not perceived by the person concerned.
Clinical symptoms
There are usually four symptoms in those affected:
- Almost complete or complete color blindness, as there are no functioning cones due to the genetic defect.
- Eye tremors (nystagmus), because there are no functional visual cells in the yellow spot (the place of sharpest vision in the center of the retina) (see retina diagram in healthy people and achromatic patients) and this defect should be compensated for by rapid eye movements.
- Hypersensitivity to light: photophobia . Rods are designed for smaller amounts of light (twilight). Since there are no functioning cones, it is not possible to inhibit the rods when there is light, in contrast to non-color-blind people.
- Significantly reduced visual acuity ( visual acuity ), as rods are arranged in a lower density in the central visual field.
Diagnosis
- The function of the rod receptors (twilight vision) and cone receptors (color vision) in the eye can be assessed separately using an electroretinogram (ERG). Flashes of light are projected onto the retina; the reactions of the sensory cells (rods and cones) are recorded by electrodes.
- A blood analysis makes it possible to examine the achromatopsia genes (see below)
genetics
- Known mutations
- CNGA3 gene (ACHM2 = Achromatopsia 2 = Rod Monochromatism 2):
- 20-30% of achromatopsia patients have mutations in this gene
- Defect: Cyclic-nucleotide-gated cation channel alpha 3 = alpha-subunit of the cone photoreceptor cGMP-gated cation channel
- Result: complete and incomplete achromatopsia
- Location: 2q11
- CNGB3 gene (ACHM3 = Achromatopsia 3 = Pingelapese Achromatopsia = Pingelapese blindness)
- 40–50% of achromatopsia patients have mutations in this gene
- Defect: Cyclic nucleotide gated channel beta subunit = beta subunit of the cGMP gated cation channel
- Location: 8q21-q22
- GNAT2 gene:
- Defect: cone photoreceptor-specific alpha subunit of transducin
- further chromosomal gene localization: ACHM1 gene
Inheritance
| Constellation of parents | Likelihood of children with achromatopsia |
Probability of healthy children |
|---|---|---|
two healthy people, including:
|
0% | 100%
|
two healthy people, including:
|
25% | 75%
|
| a clinically healthy gene carrier ( heterozygous ) and an achromatic ( homozygous ) |
50% | 50%
|
| a clinically healthy non-gene carrier and an achromatic ( homozygous ) |
0% | 100%
|
| two achromats (two homozygous gene carriers) | 100% | 0% |
Special problems of achromatic lenses
The everyday problems of achromatic lenses are primarily influenced by their high sensitivity to glare. The already poor visual acuity is further greatly reduced even in moderate light. A change in lighting conditions usually also requires a change of glasses (adapted tint or edge filter). The inability to distinguish colors also leads to difficulties in heavily color-coded everyday life.
therapy
Therapy is currently not possible for the irreversible congenital disorder of the retina. A possible gene therapy is being researched. In 2016, a test person was subjected to such a therapy at the University of Tübingen . In spring 2020, the results of a study with several test persons were published who had a defective CNGA3 gene. The team named the vector they developed as AAV8.CNGA3 (adeno-associated virus with functional GNGA3 gene). Particularly with young patients, given the right conditions, there is a good chance of success.
Specific tools
The aids are divided into three groups according to the visual problems: reducing glare, compensating for poor visual acuity, compensating for lack of color vision.
- For people with red-green poor eyesight there are special glasses that make it possible to differentiate between the colors by filtering, provided that the problem is caused by shifted absorption sensitivity maxima.
- Edge filter glasses or tinted contact lenses are required to reduce glare. Aids such as glasses with anti-glare protection against light from the side or peaked caps are also used. Edge filter glasses must be changed depending on the lighting conditions.
- Magnifying aids are used to compensate for the poor visual acuity. These are optical or electronic magnifying glasses, monocular telescopes, electronic (board) reading devices, magnifying glasses or glasses with integrated magnifying glass segments.
- Problems due to poor color recognition can, in part, be reduced by using electronic color recognition devices.
- The Eyeborg is a tool that uses a camera to convert color information into acoustic signals.
Individual evidence
- ↑ First gene therapy for a hereditary eye disease started in Germany. Press release from the University of Tübingen, June 30, 2016.
- ↑ Nadja Podbregar: First gene therapy against complete color blindness: Gene repair proves to be safe and effective in first clinical study , on: scinexx.de of May 7, 2020.
- ↑ M. Dominik Fischer, Stylianos Michalakis, Barbara Wilhelm, D. Zobor, R. Muehlfriedel, S. Kohl, N. Weisschuh, GA Ochakovski, R. Klein, C. Schoen, V. Sothilingam, M. Garcia-Garrido, L Kuehlewein, N. Kahle, A. Werner A, D. Dauletbekov D, F. Paquet-Durand, S. Tsang, P. Martus, T. Peters, M. Seeliger, KU Bartz-Schmidt, M. Ueffing, E. Zrenner, M. Biel, B. Wissinger: Safety and Vision Outcomes of Subretinal Gene Therapy Targeting Cone Photoreceptors in Achromatopsia: A Nonrandomized Controlled Trial . In: JAMA Ophthalmology . April 30, 2020, doi : 10.1001 / jamaophthalmol.2020.1032 , PMID 32352493 , PMC 7193523 (free full text).
- ↑ http://futurezone.at/digital-life/video-blas-wie-farbenblinder-vater-erstmals-farben-sICHT/130.414.996
literature
- Oliver Sacks : The island of the color blind. 1st edition. Rowohlt, Reinbek near Hamburg 1997, ISBN 3-498-06320-0 .
