At the recent celebration for Professor Irene Gottlob at the University of Leicester, Dr Frank Proudlock spoke about nystagmus and reading.
Frank commented that people with congenital nystagmus can read at the same speed as fully sighted people, provided the print is large and clear enough, that the intensity of the nystagmus does not affect reading speed, but that children with nystagmus take longer to acquire words and will need to reread new words more often. He also reported that, whilst some children say they help, in tests there seemed to be no significant advantage in using coloured overlays for reading.
Read a May 2019 article on nystagmus and reading, here.