Achromatopsia – A Hereditary Retinal Disorder

Achromatopsia (ACHM) is a condition that affects the retina, the light-sensitive tissue located in the back of the eye. It is a hereditary retinal disorder characterized by a loss of color vision on a partial or whole basis. Individuals with full achromatopsia cannot detect colors; they only see black, white, and degrees of gray. Incomplete achromatopsia is a milder version of the disease that retains some ability to distinguish colors.

Achromatopsia is also associated with additional vision issues, such as increased sensitivity to light and glare (photophobia), reflexive back-and-forth eye movements (nystagmus), and severely diminished vision sharpness (low visual acuity).

Individuals affected may also have farsightedness (hyperopia) or, less frequently, nearsightedness (myopia). These visual impairments often manifest themselves within the first few months of infancy. Achromatopsia is a stable eye disorder, which means it will not worsen over time.

Achromatopsia is distinct from more frequent color vision impairment (sometimes referred to as color blindness). Individuals sense color but have trouble discriminating between specific colors, such as red and green.

Achromatopsia is predicted to afflict one in every 30,000 persons globally. Achromatopsia in its whole is more prevalent than partial achromatopsia.

Causes and Genetic Predisposition

Achromatopsia is an autosomal recessive genetic disorder. Both gene copies in each cell carry mutations. Individuals with autosomal recessive conditions often display no symptoms since the disease is carried only by the parents, who each have one copy of the defective gene. Mutations cause achromatopsia in one or more of the following genes: CNGA3, CNGB3, GNAT2, PDE6C, or PDE6H.

Mutations in any of the genes mentioned above impair cones’ ability to respond correctly to light, interfering with phototransduction. Cones are nonfunctional in patients with full achromatopsia, and vision is solely dependent on rod activity.

Around 6 million cone photoreceptors and 120 million rod photoreceptors are found in the human retina. Under typical lighting circumstances, like during the day, cones are largely responsible for center, fine-resolution, and color vision. (Optical vision).

Cones are predominantly concentrated in the central macula, accounting for approximately 100% of photoreceptors in the fovea, the area with the best resolution and acuity. On the other hand, Rods are responsible for peripheral, low-light, and night vision (Scotopic vision) and are situated predominantly in the peripheral retina and perimacular area.

Cone function loss results in complete loss of color vision and other vision issues. Individuals with achromatopsia that is partial maintain some cone function. These individuals have restricted color vision and often have less severe vision impairments.

Certain individuals with achromatopsia have no known mutations in any of the recognized genes. The etiology of the illness is unknown in these individuals. Other unidentified genetic variables almost certainly contribute to this disease.

Diagnosing Achromatopsia

The clinical diagnosis of ACHM is made based on the patient’s medical history, visual acuity, visual field, color vision, and electrophysiological and morphological tests. Since these individuals perceive the world exclusively through their rods, the clinical results come from the absence of cone function and the presence of complete rod function.

ACHM is generally diagnosed congenitally at birth. The initial indications of achromatopsia are often an acute sensitivity/aversion to bright light and nystagmus (involuntary, repeated darting of the eyes), both of which are usually observed in children between the ages of three and six months. Poor visual acuity and reduced or nonexistent color vision will also be present; however, caregivers will not notice these signs of achromatopsia as soon.

The diagnosis is verified with an ERG (electroretinogram), which measures the inactivity of the retinal cones, a retinal examination, and, in certain cases, genetic testing. Additional testing, such as a visual field and color vision test, can be conducted as the kid grows older.

Perspectives on Therapeutics

As there is no proven therapy at the moment, dealing with social and professional implications is critical. The current standard of treatment is to manage symptoms by reducing retinal light exposure through tinted contact lenses or extremely darkly tinted sunglasses.

Typically, tinted contact lenses and cutoff filters transmit light between 400 and 480 nm, therefore alleviating photophobia. Additionally, magnifying aids and magnification contact lenses are advised to increase visual acuity. Even with the greatest external assistance measures, daily chores such as driving and attending school pose considerable challenges.

Gene therapy

Significant research has been conducted in recent years to find a viable treatment for ACHM, and the novel gene replacement therapeutic methods are encouraging. ACHM has long been considered a promising target for gene therapy due to the fact that, unlike other progressive retinal dystrophies, functional photoreceptors are likely to be retained in the majority of cases.

Gene therapy is the act of introducing, removing, or modifying genetic material-DNA or RNA-into a patient’s cells to cure them of a certain ailment. The ultimate objective of genetic therapy is to cure an inherited disease with a single treatment that corrects a faulty gene. The supplied genetic information contains instructions that modify the way the cell creates proteins.

A “vector” is used to deliver a functioning gene into the cell. Due to viruses’ superior ability to penetrate cells, they are used as vectors. Adeno-associated virus, or AAV, is an excellent viral vector for usage in various cell types, including retinal cells.

AAV is a tiny, basic virus that generates a mild immune response and has never been associated with human illness. AAV vectors have no residual viral genes, preventing the potential of any viral genes causing an unfortunate occurrence.

It is believed that the functional gene supplied by an AAV vector will remain stable for many years. Gene therapy, by treating the fundamental cause of an inherited disease, has the potential to provide a long-lasting therapeutic effect with a single vector injection.

General eye examinations are critical for persons with Achromatopsia since they may still be at risk of acquiring other types of visual disorders that affect the general population, some of which are curable.

Regardless of a person’s level of vision, it is essential to look after the eyes. Contact Arizona Retinal Specialists to schedule an eye exam or call 623 – 474 – 3937 (EYES).




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