What is Achromatopsia?
Achromatopsia is a retinal condition that results in the inability to see color. Complete achromatopsia prevents a person from seeing color; they only see black, white, and varying shades of gray. Individuals with incomplete achromatopsia, a less severe variation, may have some color vision.
Achromatopsia is a rare autosomal recessive inherited retinal disorder that affects 1 in 30,000 individuals. Achromatopsia also causes individuals to be light sensitive, have reduced vision and uncontrolled eye movements.
- Achromatopsia is a disorder of the cones that make up the retina, which sends visual signals from the eye to the brain.
- Retinal achromatopsia occurs when both parents carry a copy of the mutated gene.
- Achromatopsia can be inherited genetically or acquired due to brain damage.
Phototransduction is responsible for sending visual signals from the retina to the brain. The retina is made of two different classes of light-receptor cells called rods and cones. Rods function in low-light vision, such as at night, and cones are responsible for color vision, and visual acuity/clarity.
If the cone cells malfunction, they lose their ability to signal to the brain. This limits the process of phototransduction. In complete achromatopsia, the cone cells do not function, and signals are only transferred through rod cells. In incomplete achromatopsia, people retain some cone cell function.
Achromatopsia can be distinguished from more common forms of color blindness by the fact that all three types of cones are defective.
How Is Achromatopsia Acquired?
It is inherited when an individual acquires two copies of the defective gene—one from each parent. The defective gene is present in both parents of an individual with achromatopsia, but they normally do not exhibit the signs and symptoms of the disorder because their functional or “good” gene counteracts the defective gene. However, when both of those parents have a child, that child may get a defective gene from both parents.
In most circumstances, a person who gets one normal gene and one defective gene will not have visual symptoms. but will just be a carrier. A carrier means the individual is carrying a defective copy of the gene but does not have the condition.
Cerebral achromatopsia can be acquired and is different from retinal achromatopsia. Cerebral achromatopsia is an acquired color blindness due to brain damage from trauma, tumors or infections.
What Are The Types Of Achromatopsia?
There are two types of Achromatopsia, total and incomplete.
- Complete – The patient does not have any functional cones and experiences severe visual problems.
- Incomplete – The patient has some functional cones and experiences less severe visual complaints. Incomplete achromatopsia is also called rod monochromacy.
What Are The Symptoms Of Achromatopsia?
Symptoms of achromatopsia begin to manifest during the first few months of life, and include:
- Reduced visual acuity
- Hemeralopia (day blindness)
- Nystagmus (uncontrolled eye movements)
- Lack of color discrimination
Currently, there is no proven treatment for achromatopsia. However, there are tools available to help patients navigate visual impairment, including magnifiers for poor vision and deep red-tinted glasses or contact lenses to lessen symptoms of light sensitivity.