Achromatopsia – seeing the world without colour
This post is the first in a series of three blog posts about the inherited retinal condition called achromatopsia. Read on to also learn about the condition first hand from an interview with one of our patients.
I am writing about achromatopsia because Professor Michel Michaelides at Clinica London specialises in inherited retinal diseases and he also knows an awful lot about achromatopsia. He can advise you on the diagnosis, whether you have it or not, and what possible effects it can have on your life. He will also advise you on what practical measures you can take to minimise the effects such as photosensitivity and having a complete absence of colour vision and with a little bit of shaking of the eyes, called nystagmus.
In this series of three blog posts, we’ll cover
- what achromatopsia is
- an interview with Shahlaa, who has achromatopsia and is successfully pursuing a university degree,
- Significant advances in research for gene therapy for achromatopsia.
What is achromatopsia?
You may have achromatopsia, which we often call ‘day blindness’ if as a child you found that you could see a lot better in subdued light. With achromatopsia, you have no colour vision. You are sensitive to light (photophobia), and you have the presence of nystagmus (shaking of the eyes). Achromatopsia is a relatively rare condition affecting approximately 1 in 30,000 live births. It is a genetic condition, so it is going to be higher in regions of the world where there is a higher rate of consanguineous marriages, i.e., marriages between relatives, and also specifically in isolated areas such as in the Eastern Pacific Islands of Pingelap. Please see a book by Dr Oliver Sacks called The Island of the Colorblind. It is non-progressive. It is a hereditary visual disorder.
Its three characteristics are:
- decreased vision, particularly in bright light
- light sensitivity
- the absence of colour vision
Note that it is not the same as red-green colour blindness. If you just have red-green colour blindness, which affects 8% of all males, you do not have achromatopsia. It is not the same condition because people who have red-green colour blindness have otherwise completely normal visual acuity, and they lack the complete loss of colour vision, light sensitivity and wobbling or shaking eyes.
The problem is in the retina, which is the part of the eye that helps to make the picture of the world and affects the cells called cones, which are responsible for normal colour vision.
You may not know, but you have red cones, green cones and blue cones, with a particular distribution for normal colour vision. Cone cells concentrate in the most sensitive part of the retina called the macula and fovea. In achromatopsia, these cones are non-functioning when
the child is born. Some children may have a residual degree of cone function and are said to have incomplete achromatopsia.
Genetic research into achromatopsia, an inherited retinal condition, has shown that there are six genes identified to date: CNGA3, CNGB3, GNAT2, PDE6C, PDE6H and ATF6.
You can inherit achromatopsia if both your mother and father carry a fault in one of these genes. Your parents do not develop the disease because to develop the disease requires that the affected person has a fault in both copies of the gene. We call this inheritance pattern autosomal recessive. A family with one affected child has a 25% risk of each pregnancy carrying an affected offspring and a 50% chance that the child will be born as a carrier.
What will happen when you meet Professor Michaelides?
Professor Michaelides will make the clinical diagnosis of your achromatopsia. He will base this determination on your history and further tests. He will look at your retina, and it may appear completely normal. He will do colour vision tests, including the Ishihara colour vision testing. He may arrange for you to have electroretinography (ERG). Optical coherence tomography (OCT) and fundus autofluorescence imaging are also useful screening tools for achromatopsia.
If you think that you or your child may have achromatopsia, you should make an appointment to see Professor Michaelides at Clinica London who will examine and advise you.