The achromatopsia is a vision defect in which the person who has it is not able to distinguish colors. A condition also known by the name of monochromatic vision, it is characterized by perceiving only the colors white, gray and black, as well as their tones.
The ability to not distinguish colors in patients with achromatopsia can be total or partial. In addition, they present other problems such as decreased visual acuity, involuntary movements of the eyes or nystagmus, sensitivity to light or photophobia and inability to fix vision to a point.
Vision of a person with achromatopsia (left). Normal vision (right). By Mfrost88 - Own work, Public Domain, This inability to distinguish color can be genetic or acquired. When it occurs from birth due to genetic abnormalities, the problem is in the color perception cells located in the eyes called cones.
On the contrary, in the case of an acquired condition, the problem is found centrally, in the signal transmission pathways from the eyes to the brain, frequently as a consequence of trauma or ischemic vascular disease. These patients do not have eye dysfunctions.
The treatment of this condition is based on measures to improve the quality of life of the patient, since there is no cure.
Causes
The causes of achromatopsia can be genetic or acquired. If they are genetic, they appear from birth, being a rare condition, since it is a genetic mutation that only occurs in 1/30,000 individuals. In the case of being acquired, the underlying disease must damage the specific part of the cerebral cortex that interprets colors.
Congenital
Patients with genetic achromatopsia have a dystrophy in the cells of the eyes that are responsible for perceiving colors and sending signals in the form of electrical impulses to the brain where they are interpreted. These cells are called cones and are located in the retina.
The problem in the cones is mediated by specific genes that act at this level during the formation in the fetus.
There are 3 types of cones: those that are sensitive to the color red, those that are sensitive to the color blue and those that are sensitive to the color green. The type of dysfunction that the patient has will depend on the group of cones that is atrophied.
Eye cell cone. From Ivo Kruusamägi - Own work, CC BY-SA 3.0, The most common is that the person is unable to distinguish all the colors, therefore they will have a vision in black, black and gray scale. This type of achromatopsia is called complete or typical color blindness.
Normal vision By Q-lieb-in - Own work, CC BY-SA 4.0, 
Vision of the patient with tritanopia. By Tohaomg - Own work, CC BY-SA 4.0, There is also a partial or incomplete type, atypical, in which the patient cannot distinguish a specific color.
The partial type takes on specific names to refer to each condition. Thus, the dystrophy of green perception cones is called: deuteranotopia; the one with red perception cones is the protanotopia and the one with blue perception cones is tritanotopia.
Acquired
Acquired achromatopsia is secondary to an external cause that causes damage to the cerebral cortex, specifically in the part specialized in interpreting colors.
It can occur from severe head trauma, but is usually the consequence of ischemic cardiovascular disease that causes decreased or absent vascularization in that brain area.
These patients do not have eye problems and their vision is normal until the time of the accident that caused the brain damage.
In this type of achromatopsia the symptoms are different from those found in a patient with genetic disease. It is often accompanied by other perceptual disorders such as the inability to recognize familiar faces or prosopagnosia.
Symptoms
Patients with achromatopsia present from an early age involuntary movements of the eyes in a horizontal plane, called nystagmus; also a decrease in visual acuity, which is the sharpness with which images are observed under adequate lighting conditions.
They are also very sensitive to light, presenting the disorder called photophobia and may have blurred vision under very bright lighting or hemeralopia.
The inability to identify colors can be partial or total, but the most common is that it is complete and the person perceives all the colors in the gray scale.
Color scale according to the pathology. By Nanobot - Own work, Public Domain, In partial achromatopsia, the patient presents all the symptoms of his total counterpart, but with less intensity.
Diagnosis
The diagnostic approach can be made by the specialist in a child with nystagmus, or movement of the eyes, when other causes of this symptom are ruled out.
A full ophthalmologic evaluation should be performed later in which visual acuity and color perception are examined.
To assess a person's ability to distinguish colors, a test is used in which a series of cards with specific designs for this purpose is observed. They are called the Ishihara letters.
Ishihara's letters. By https://wellcomeimages.org/indexplus/obf_images/70/0e/6d5cf7d381b3a0a05b8a9761f2b9.jpgGallery: https://wellcomeimages.org/indexplus/image/L0059165.htmlWellcome Collection gallery (2018-03-29): https: // wellcomecollection.org/works/whqvsube CC-BY-4.0, CC BY 4.0, The cards were designed by the Japanese ophthalmologist Shinobu Ishihara in 1917. The drawing consists of a circular image that in turn contains small colored circles inside, which draw a number on the red and blue scales.
The card game consists of 38 cards, but clutter is usually spotted quickly when testing begins.
Vision of the cards according to the vision disorder. By Eddau processed File: Ishihara 2.svg by User: Sakurambo, with http://www.vischeck.com/vischeck/vischeckURL.php - File: Ishihara 2.svg by User: Sakurambo, processed by http: // www. vischeck.com/vischeck/vischeckURL.php, CC BY-SA 3.0, The definitive diagnosis of achromatopsia is made from a genetic test that reveals the mutation.
Treatment
Currently there are no treatments to cure achromatopsia, although there are studies in the experimental phase in which intraocular injections of specific factors that help to regenerate the activity of the cones are made.
Patients with achromatopsia present bothersome symptoms such as photophobia and hemeralopia, for which the use of contact lenses with special filters is indicated to improve their vision during the day.
Visual acuity problems improve with the use of lenses with specific formulas for each case.
Children with achromatopsia should go to a specialized consultation every 6 months and adults between 2 and 3 years.
Despite the proper application of these treatments, patients with difficulty distinguishing colors have problems carrying out common activities such as driving and attending a class at school.
Genetic counseling with a specialist is recommended for people who have the disease, or whose parents have it, at the time of family planning. This will explain the risks and chances of having a child with the condition.
References
- Kohl, S; Jägle, H; Wissinger, B. (2018). Achromatopsia. StatPearls. Treasure Island (FL). Taken from: ncbi.nlm.nih.gov
- Aboshiha, J; Dubis, A. M.; Carroll, J; Hardcastle, A. J; Michaelides, M. (2016). The cone dysfunction syndromes. The British journal of ophthalmology. Taken from: ncbi.nlm.nih.gov
- Hassall, M. M; Barnard, A. R; MacLaren, RE (2017). Gene Therapy for Color Blindness. The Yale journal of biology and medicine. Taken from: ncbi.nlm.nih.gov
- Johnson, S; Michaelides, M; Aligianis, I. (2004). Achromatopsia caused by novel mutations in both CNGA3 and Journal of Medical Genetics. Taken from: jmg.bmj.com
- Pang, J. J; Alexander, J; Lei, B; Deng, W; Zhang, K; Li, Q; Hauswirth, WW (2010). Achromatopsia as a potential candidate for gene therapy. Advances in experimental medicine and biology. Taken from: ncbi.nlm.nih.gov