Achromatopsia is a rare and hereditary visual disorder caused by the absence or impairment of functional cones in the retina. There are two types of Achromatopsia: complete and incomplete. The complete Achromatopsia enables people to see only white, black and many shades of grey, without perceiving any colours. Complete Achromats have no functional cones in the retina and suffer from severe visual aberrations. On the other hand, the incomplete type of this disorder is much milder and connected with discrimination of some colours. The incomplete Achromats have some functional cones in the retina and less severe visual symptoms. Achromatopsia is a non-progressive disorder, related to several other problems with vision, such as photophobia, nystagmus and low visual acuity. Achromatopsia, also known as monochromacy, is a type of colour blindness. A non-profit Colour Blind Awareness’ Community compares Achromats’ visual experience to “seeing the world on an old black and white television set”1 and presents Achromats’ vision among other types of colour blindness, such as Trichromacy and Dichromacy (see Types of Colour Blindness*).
Causes
Achromatopsia is a genetic disorder of the retina – a part of the eye which consists of rods and cones. These light receptor cells are responsible for transmitting visual signs to the brain, providing night and daylight vision, including colour vision, which is enabled by red, green and blue cones. Because of congenital mutations in genes CNGA3, CNGB3, PDE6C, PDE6H, GNAT2, OPN1LW or OPN1MW2, cones cannot function properly, which leads directly to Achromatopsia. Losing their functionality, cones do not participate in transmitting visual signs from the eye to the brain – the process is thus entirely operated by rods, which results in lack of colour vision and emerging of other severe visual symptoms. It is notable that cones of incomplete Achromats do not lose their function entirely, enabling people to see a limited number of colours and decreasing the severity of other visual problems. It is estimated that 75% of Achromatopsia cases are caused by mutations in genes CNGA3 and CNGB33.
Symptoms
Symptoms of Achromatopsia appear in the first few months of life and can be observed by parents of the child with non-functioning cones. First, the child avoids daylight, which is the symptom of photophobia – an increased sensitivity to light connected with strong discomfort or eye pain during the exposure to daylight. Second, the uncontrolled, repetitive, back-and-forth eye movements occur, which are diagnosed as nystagmus. The third most common symptom of Achromatopsia is low visual acuity (far-sightedness, near-sightedness or astigmatism), which may be observed by parents during a child’s daily activities. The symptoms slightly differ between complete and incomplete Achromatopsia. It is assumed that the incomplete Achromatopsia’s symptoms are similar but less severe than the symptoms of complete disorder. The incomplete Achromats rarely suffer from photophobia and nystagmus, have better preserved visual acuity and can distinguish specific colours. For example, incomplete Achromats with functioning red cones can detect the red colour while looking through the right filter4.
Frequency of appearance
Achromatopsia is an uncommon disorder which affects about 1 in 30,000 people from all over the world5. Considering its genetic connection, in some parts of the world the disorder is more frequent than in others. Dr Oliver Sacks in his book “The Island of the Colorblind” proves that many Achromats can be found in the eastern Pacific islands of Pingelap (4-10% of Pingelapese are Achromats6), where marriages between relatives are common. Interestingly, “Pingelapese blindness” is one of the terms used in reference to the complete Achromatopsia7, which indicates the commonness of the disorder among the inhabitants of Pingelap. The Pingelapese mostly suffer from many symptoms of complete Achromatopsia, such as horizontal nystagmus, photophobia, colour blindness, myopia, cataract and amaurosisiv8.
Diagnosis
Having the symptoms of Achromatopsia, there is a need to make a diagnosis by an ophthalmologist. The diagnosis consists of several colour vision tests, for example, HRR Pseudoisochromatic Plate Test, Ishihara Colour Plate Test, City University Test, D-15 or Farnsworth-Munsell 100 Hue. One of the most common is the Ishihara Colour Plate Test, which can be used for both children and adults. The Ishihara test consists of numbers made out of dots and surrounded by dots in different colours (check online Color Blind Test). Since Achromats and people with other colour vision deficiencies cannot indicate the numbers, the test in an easy and fast way allows us to determine whether we struggle with colour blindness or not. To confirm the diagnosis, the doctors often use well-tried eye tests such as electroretinography (ERG) or optical coherence tomography (OCT), which allow detecting retina’s functions by displaying waveforms shape specific to Achromats (ERG) or dysfunction of cones in the centre of the retina (OCT). However, a genetic test is the only 100% effective method to confirm Achromatopsia9. It is also performed to diagnose the mutations in the genes which are most vulnerable to genetic changes. If you are looking for more information about diagnosing and testing Achromatopsia, see The Diagnosis of Achromatopsia*.
Treatment & Support
Achromatopsia is a non-progressive and hereditary disorder with no available methods of complete healing. Achromatopsia treatment focuses on decreasing the symptoms by using glasses and contact lenses. Glasses are recommended for Achromats with myopia, hyperopia and astigmatism to provide better levels of vision. There are also prescription glasses with red-coloured hard lenses which help reduce symptoms of photophobia. However, the glasses are often described by Achromats as uncomfortable, so they much more willingly choose contact lenses for Achromatopsia. The tinted contact lenses are available in 5 colours (bright orange, orange, red, flame red, brown) and a pair can be used for a quarter or a year. The undoubted advantage of contact lenses is the ability to use them separately or in addition to regular dark sunglasses. Although Achromatopsia cannot be cured, there are effective ways to cope with its symptoms. Apart from dark glasses and tinted contact lenses, which deal with photophobia and improve visual function of Achromats, there are also other useful devices that improve the lives of patients. Achromats can download multiple mobile and desktop applications, e.g. colour recognition apps, GPS apps with talking maps and warning alarms, or speech-to-text converters (see iPad/iPhone Apps for Achromats). Optical aids are mostly designed for school children who usually attend mainstream schools. Children can use scopes, magnifiers, monoculars and other devices which we precisely described here*. To facilitate learning, school children should be also provided with large print books, front seats and other available aids for Achromats.
Sources
American Association for Pediatric Opthalmology and Strabismus. 2019. Achromatopsia. [accessed 2020 Feb 14]. https://aapos.org/glossary/achromatopsia
Low Vision Centers of Indiana:
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(n.d.). Colorblindness and Achromatopsia. [accessed 2020 Feb 14]. http://www.achromatopsia.info/color-blindness/
(n.d.). The Diagnosis of Achromatopsia. [accessed 2020 Feb 14]. http://www.achromatopsia.info/diagnosis-testing/
Colormax. 2020. Color Blind Test. [accessed 2020 Feb 14]. https://colormax.org/color-blind-test/
Colour Blind Awareness. (n.d.). Types of Colour Blindness. [accessed 2020 Feb 14]. http://www.colourblindawareness.org/colour-blindness/types-of-colour-blindness/
Fighting Blindness. 2019. Achromatopsia. [accessed 2020 Feb 14]. https://www.fightingblindness.ie/living-with-sight-loss/eye-conditions/achromatopsia/
Genetics Home Reference. 2020. Achromatopsia. [accessed 2020 Feb 14]. https://ghr.nlm.nih.gov/condition/achromatopsia
Kohl S., Jägle H., Wissinger B., Zobor D. 2004. Achromatopsia. [accessed 2020 Feb 14]. https://www.ncbi.nlm.nih.gov/books/NBK1418/
Sacks O. 1997. The Island of the Colorblind. New York: A. A. Knopf.
Shiel Jr. William C. 2018. Medical Definition of Achromatopsia. [accessed 2020 Feb 14]. https://www.medicinenet.com/script/main/art.asp?articlekey=11286
1http://www.colourblindawareness.org/colour-blindness/types-of-colour-blindness/
2https://www.ncbi.nlm.nih.gov/books/NBK1418/
3https://www.fightingblindness.ie/living-with-sight-loss/eye-conditions/achromatopsia/
4http://www.achromatopsia.info/color-blindness/
5https://aapos.org/glossary/achromatopsia
6https://www.medicinenet.com/script/main/art.asp?articlekey=11286
7https://www.ncbi.nlm.nih.gov/books/NBK1418/#
8https://www.medicinenet.com/script/main/art.asp?articlekey=11286
9https://www.fightingblindness.ie/living-with-sight-loss/eye-conditions/achromatopsia/