The College of Optometrists

 

The man who gave his name to colour blindness - "Daltonism" was neither an optician nor a physician but a chemist!

  

Chemical colour vision test - a set of 22 test-tubes with cork stoppers containing various coloured chemicals including Iodine of Mercury and Carmine (20th century)

John Dalton (1766-1844) described his own colour vision deficiency - seemingly the first ever account of living with the condition -in a paper entitled Extraordinary Facts Relating to the Vision of Colours with Observations given to the Manchester Literary and Philosophical Society on 31 October 1794 (later published in 1798). In this paper Dalton described how, in 1790, a study of botany had caused him to pay more attention to colours, the nomenclature of which had always given him problems. He had remembered, however, reading an article back in 1777 about a fellow Cumbrian, Mr Harris of Maryport, who 'could not distinguish colours' and had contacted the family as part of his study.

 

Dalton saw only the blue, violet and yellow parts of the spectrum correctly.

  

That part of the image which others call red, appears to me little more than a shade or defect of light; after that, the orange, yellow and green seem one colour, which descends pretty uniformly from an intense to a rare yellow, making what I should call different shades of yellow

 

In a letter written by Dalton to Elihu Robinson in February 1794 he claims to have discovered his colour blindness 'last Summer' and had been collecting silk ribands in various colours from a friend who was a dyer in order to compare his perceptions with those of his acquaintances. During these discussions he had mistaken for red a coat which was grassy green and described a pink flower as 'sky blue' in daylight but 'red' by candlelight. He had discovered that only his brother shared the same perception and concluded that the two of them had an hereditary 'coloured medium' or blue colouration in the humour of the eye.

 

In order to test his theory he graciously donated his own eyes to medical science after his death. The doctor Joseph Ransome removed the eyes the day after he died and quickly disproved the colouration theory. Dalton had been in error!

 

More excitingly, Ransome left one of the eyes intact, thus enabling Mollon, Dulai and Hunt, after a gap of two centuries (1994), to take a retinal sample and conduct a DNA analysis. They have claimed that this project was the first instance where an hereditary defect has been identified in an historic figure, allowing the compilation of a 'molecular biography'. They even conducted analysis on the types of flowers and even the eighteenth century sealing wax that Dalton had described in his writings. Mollon, Dulai and Hunt concluded that Dalton had in fact been a deuteranope with a single long wave (LW) opsin gene coding for an LW visual pigment.

 

Daltonism

 

Although he was not the first to investigate colour blindness the name of Dalton  has been used to describe the condition in many countries ever since, even in  languages such as Spanish and Russian. Dalton himself appears not to have  minded. The word was popularised in print from an early date, being traceable to Prevost of Geneva who referred to daltonien in 1827.