Achromatopsia refers to a rare hereditary disease where a person has a partial or total absence of color vision. The condition manifests in two forms; complete and incomplete achromatopsia. Children with the complete type see their world as only white, grey, or black, while those with incomplete achromatopsia may have a little color discrimination (they can distinguish subtle differences in color).
Complete achromatopsia is more common than the incomplete type. Incomplete achromatopsia patients often have better vision and less visual symptoms. Because achromatopsia does not progress, vision may stabilize over time. Achromatopsia is different from color blindness, where people perceive colors but cannot distinguish between colors, such as green and red.
Also Known As
- Total color blindness
- Rod monochromatism
Causes & Risk Factors
The retina contains both rods and cones, which relay visual signals from the eye to the brain in the phototransduction process. Achromatopsia arises in children born with non-functional cones.
It is caused by mutations of the CNGB3, CNGA3, ATF6, PDE6H, PDE6C, and GNAT2 genes. Retinal cones do not react appropriately to light due to these mutations.
The rods help people to see at night since they offer vision in low light. On the other hand, cones help absorb different color lights and provide vision in bright light. The color lights absorbed include the red, green, and blue cones, which need to be distributed appropriately to enable normal color vision. If the cone function is lost, the affected person will experience a total lack of color vision and may have other problems with vision.
Children with complete achromatopsia have non-functioning cones so that their vision depends completely on the rods. Those with incomplete achromatopsia have a little cone function.
The risk factors may include:
- Marriage between relatives
- Geographic locations such as Micronesia, especially among Pingelapese islanders
In some children, the cause remains unknown because they lack identified gene mutations.
Signs & Symptoms
Signs and symptoms develop in the first few months of life and may include:
- Reduced or blurry vision
- Hyperopia or farsightedness
- Partial or total color blindness
- Sensitivity or dislike for bright lights
- Myopia or nearsightedness, though not common
- Nystagmus or involuntary, rhythmic eye movements
Achromatopsia may be diagnosed in the following ways:
- Genetic testing to help confirm the diagnosis
- Color vision tests such as the H-R-R tests, Ishihara pseudoisochromatic tests, etc
- Visual acuity test using a Snellen chart where people are asked to read some letters on the chart
- Taking down medical and family history, especially where genetic involvement may be suspected
- An examination that involves identifying symptoms such as sensitivity to light. The retina is also assessed
- Imaging tests and others such as optical coherence tomography, electroretinogram, fundus autofluorescence, and visual field tests which can help to measure cone function, identify the damage, or assess the back of the eye
There is currently no treatment available for treating achromatopsia. However, the symptoms may be alleviated through:
- The use of tinted or red-colored lenses which can enhance visual functioning by reducing photophobia
- Low vision devices such as magnifiers and telescopes which can enable the person to lead a normal school, work, or daily life
- Eyeglasses and contact lenses can help treat refractive errors such as hyperopia, myopia, and astigmatism. Vision may be improved but will not be fully restored to normal levels
Prognosis & Long-Term Outlook
Children with achromatopsia will have to live with the condition. They need adequate assistance from teachers trained to handle the visually impaired. This will enable achromatopsia patients to attend a normal school. A child with achromatopsia will be made to occupy the front seats, read from large print books, and use magnifying devices when there is need. The child needs to undergo a low vision test before school starts. If the disorder is severe, the affected child is referred to special schools for the visually impaired.
Prevention & Follow Up
Children with achromatopsia may carry the risk of developing other treatable problems of the eye. Therefore, regular general check-ups are recommended for them.