AFAIK there is no medical requirement at all for a French microlight license. I'd like to be sure though, since I wish to go for that license this year. Not that is really an issue for me, just a point of administrative concern.
NB do not be confused by the difference in definitions: what is called a microlight in the UK and an ultralight in Europe is (more or less) an LSA in the USA, and typically seats two. The US'an ultralight is indeed "ultra" light and can only carry its pilot.