Twenty-one years ago, when I was a young Labour MP, I wrote a piece in these pages about going blind. I described a rare degenerative eye condition called choroideremia, which shrinks and darkens one’s vision until eventually there’s nothing left. I started to see less in my late teens; by the time I wrote the piece in 2002 I was 33 and perhaps half-blind, but could still manage to do most things pretty well.