From Barry Cash
The article on improving vision (23 May, p 33) reminded me of spending two years in my early 20s matching colours in a laboratory. At the medical before my next job, to doctors’ surprise I could read both the numbers I should be able to see in the Ishihara colour vision test and the numbers I should not. I put this down to the two years that I spent looking intently for differences in colours.
Bristol, UK
