When referring to abnormal colour vision eye care professionals are trained to use the term ‘colour deficiency’, in preference to the traditional phrase ‘colour blindness’ which implies seeing only in black and white. Whereas colour deficiency is relatively common (8% of males, 0.5% of females), true colour blindness, or achromatopsia, is much rarer. Congenital achromatopsia is estimated to affect one in 30,000 people. How remarkable, then, to find a tiny island in the western Pacific where between one in 25 and one in 10 people are affected by the condition.
Achromatopsia is a congenital hereditary condition that has two forms. The more common variety is rod monochromatism, an autosomal recessive condition, requiring both parents to pass on a defective gene, and is seen more or less equally in males and females. Blue cone monochromatism, actually a form of incomplete achromatopsia, is an x-linked recessive condition that is much rarer, affecting around one in 50-100,000 males and possibly only one in 10 billion females.
While rod monochromats have a complete absence of cones, blue cone monochromats – as the name suggests – have cones which are sensitive to the blue end of the spectrum. The latter have very limited colour vision and may report that blue objects are more distinct, even if their perception of ‘blueness’ is not the same as a colour-normal person. One might expect that the complete absence of colour in rod monochromats means that these people see the world in black and white and shades of grey. But the concept of ‘greyness’ only really makes sense in the context of one who is able to appreciate lack of colour; to someone who has never experienced colour, the term is meaningless. Rod monochromat, Frances Futterman, (quoted on the achromatopsia.info website) once explained: ‘No one was going to convince me that everything in the world I knew to be so richly varied in shades of light and dark was all supposed to be called “grey”! To me, it seemed ridiculous to imagine that, for instance, a dark tree and a light-coloured flower would both be identified as “grey.” If I could see – or if I had ever been able to see – any colours, then I might perceive the absence of colour as grey.’
A very close study of an atlas is needed to find the tiny island of Pingelap, a curious coral atoll in the Pacific Ocean that has an unusually high incidence of rod monochromatism. Located to the north of New Guinea, it is part of the Federated States of Micronesia which itself comprises the eastern part of the Caroline Islands, an archipelago of around 500 islands so named after the Spanish king, Charles II, by Spanish explorers who discovered them in the 15th century. How has something approaching a tenth of the population of Pingelap come to have a condition that affects only one in 30,000 of the general population?
Typhoon disaster
The root of the conundrum can be traced back to typhoon Liengkieki which devastated Pingelap in 1775. The storm and resulting famine wiped out most of its population. Only around 20 islanders survived, including the king or ruler, Nahnmwarki Mwanenised. It is thought he had a defective gene and was therefore a carrier of rod monochromatism. The typhoon disaster created what is known as a population bottleneck; the subsequent inbreeding within such a small population in part due to remote geographic location and an isolationist culture gave rise to a ‘founder effect’, a loss of genetic variation that results from population growth from a small number of founding individuals. It is believed that the king was the only carrier of the defective gene among the survivors so, because of the autosomal recessive nature of the condition, the rod monochromatism did not become manifest until the fourth generation after the typhoon.
The story of the Pingalepese rod monochromatism took another step back in time once the gene for the condition was identified in 2000 by researchers at Johns Hopkins University. They mapped the gene to chromosome eight (8q21-q22). The same gene is found in those of Irish descent, so it is speculated that a sailor of Irish heritage may have introduced the gene to the island. The Pingalapese condition is characterised by total colour blindness, nystagmus, low visual acuity and photophobia. Sufferers report being able to see better in low levels of light. A team of researchers from Israel travelled to Pingelap to investigate another feature of the condition called paradoxical pupillary response, also known as ‘Flynn phenomenon’. It is described as a response whereby, after exposure to light for two to three minutes, on then transferring to darkness the pupils constrict.
While not unique to rod monochromatism (it is seen in other diseases such as Leber’s congenital amourosis, congenital stationary night blindness and congenital nystagmus), the Israelis found that it was present in 23 of 27 subjects examined. Their findings are reported in ‘Pingelapese achromatopsia: correlation between paradoxical pupillary response and clinical features’ (Ben Simon, Abraham and Melamed, Br J Ophthalmol 2004;88:223–225).
An earlier investigation of the Pingelapese was undertaken by the renowned neurologist, Oliver Sacks, author of, among other publications, Awakenings and The Man Who Mistook His Wife For a Hat. He had been introduced to achromat and scientist, Knut Nordby, by Frances Futterman, founder of the Achromatopsia Network (who was quoted above). Sacks and Nordby decided to go to Pingelap, along with ophthalmologist, Bob Wasserman, to see for themselves the achromatic people they had been told about. Their experiences were retold in Sacks’ book, The Island of The Colour Blind (1997), which brought the islanders’ story to a worldwide audience.
Born to be wild
Not that achromatopsia need be a barrier to a full and successful life. The story of Joachim Fritz Krauledat is a case in point, an achromat who also had to overcome many other difficulties along the way. Having changed his name to John Kay in his teens – still not exactly a household name – he is better known as the founder and frontman of the rock band Steppenwolf, who shot to fame after their anthemic track Born To Be Wild was used on the soundtrack of the 1969 film Easy Rider. He was born in the small town of Tilsit, East Prussia, in 1944 two months after his father, a German soldier had perished on the Russian front. Fearing the advancing Russians, his mother managed to get them both to eastern Germany which, ironically, came under Russian control at the end of the war. She had very soon become aware of baby John’s nystagmus and aversion to bright light.
There was limited optical care available but he was given prescription tinted spectacles. Achromatopsia was never suspected, being such a rare condition. John was four years old by the time his mother had scraped together enough money to be able to afford to hire a guide to smuggle them to West Germany.
Ten years later, his new stepfather decided the family would emigrate to Canada for a better life. John was faced with attending a school that taught in a language he could not speak and which did not at first understand his visual problems. John recalls, ‘Even though I was in the front row, I now had to decipher the handwriting of someone writing in an unusual handwriting style, in a language I didn’t understand, all from a distance I couldn’t see from.’ Music became a displacement activity for the games lessons that, because of the bright daylight, he could not take part in. In 1963 the family moved again, to Buffalo, New York. There he formed his first band, the start of a music career that would lead to his success with Steppenwolf.
The Pingelapese, too, find ways to circumvent the difficulties that maskun (meaning ‘no-see’ in the Pinelapese language) causes. Some of the fishermen fish at night, when their vision is better, catching flying fish that are attracted to flaming lanterns hung from their boats. And, as one of the subjects of the Israeli study pointed out to the researchers, ‘We don’t just go by colour, we look, we feel, we smell, we know – we take everything into consideration, and you just take colour!’
Oliver Sacks came up with a very interesting observation in his book, on how technology has changed the social outlook of achromats who (apart from the Pingelapese) may never come into contact with a fellow sufferer: ‘Perhaps this new network, this island in cyberspace, is the true Island of the Colourblind.’
