What is Achromatopsia?
Achromatopsia is sometimes called ‘Day Blindness’ as these children see better in subdued light. Achromatopsia is a non-progressive and hereditary visual disorder which is characterized by decreased vision, light sensitivity and the absence of colour vision. Children with complete achromatopsia will have reduced vision (20/200 or less) due to an abnormality of the retina. Children with incomplete or partial achromatopsia may have better vision (20/120 to 20/80).
What causes Achromatopsia?
Achromatopsia is caused by an abnormality of the cone cells of the retina, the portion of the eye responsible for “making the picture”. In the retina, there are three types of cone cells that are responsible for normal colour vision. These are the red cones, the green cones, and the blue cones. A balanced distribution of these cells is necessary for normal colour vision. A child born with non-functioning cones will have achromatopsia. Sometimes children have a reduced complement of cones, in which case they will have partial or incomplete achromatopsia.
How is Achromatopsia inherited?
Achromatopsia is inherited in an autosomal recessive fashion. This means both the mother and father carry the diseased gene. A family with one affected child has a 25% (1 in 4) risk of each pregnancy carrying an affected offspring. There would also be a 50% chance that a child could be a carrier.
How is the diagnosis made?
The diagnosis would be made by an ophthalmologist. Initially, symptoms such as light sensitivity and reduced vision will provide clues essential to the diagnosis. The retinal examination may in fact be normal. The diagnosis can be confirmed by electroretinography (ERG). Also, new advances in retinal imaging gives ophthalmologists better tools to evaluate the condition.
What treatment is available for Achromatopsia?
Currently there is no treatment for achromatopsia. Research on gene therapy is ongoing and may lead to clinical treatments in the future. Children with achromatopsia should be checked for refractive errors (need for glasses). Prescribing glasses to correct refractive conditions such as far-sightedness (hyperopia), near-sightedness (myopia) and astigmatism can improve the vision somewhat but will not restore normal levels of vision. Red coloured lenses help reduce the sensitivity to light and thus enhance visual functioning of individuals affected by achromatopsia.
Behaviours or conditions that might indicate Achromatopsia
- Eyes may wobble or show involuntary movement (nystagmus), though this may diminish with age.
- Colour naming and recognition may be delayed.The child will have an absence of colour vision and will be only able to perceive black, white and grey shades of colour (this would not apply to children with partial achromatopsia).
- The child may have trouble with certain activities or school work that requires them to use colour.
- The child will have decreased acuity of vision.The severity will depend on the type of achromatopsia.
- The child may be sensitive to bright light, though this may improve with age.
- The child may also experience a refractive error and may require prescription glasses.
What to do
- The young person should visit an optometrist or ophthalmologist to determine diagnosis and cause and possible prescription lenses. Red coloured lenses may be prescribed to help reduce the sensitivity to light and thus enhance visual functioning.
- A Functional Vision Assessment will assess the infant, child or young person’s use of vision. This will include observations and assessments of how he/she uses vision in real life situations and for learning and access to Te Whāriki, the New Zealand Curriculum, the Blind and Low Vision Education Network, NZ (BLENNZ) Curriculum and the Expanded Core Curriculum. Adaptations or modifications to the environment and materials used may be required. Some of these can include lighting review and seating, monitoring glare to reduce fatigue and maximise access and defining spaces to encourage play and movement. Strategies and suggestions for low and high tech devices later in life to assist the learner’s functional vision are also included in the functional vision assessment. Some of these strategies can include a review of print size, contrast levels and the effects of clutter. When colour is a component to school work such as in art, labelling paints and coloured art supplies can help as well as writing out the names of colours if they are relevant to instruction.
- A Developmental Orientation and Mobility assessment will assess how the infant, child or young person moves purposefully, safely and confidently in the environment and how they understand where they are in space and what is around them.