The bad eyesight is congenital cataracts, nystagmus is just something you tend to exhibit if you've had them, it's not noticable most of the time). I'm not sure what the cause of Blunkett's blindness is, but I believe he exhibit nystagmus as well, as does (I seem to remember) the head of the Foundation for Information Policy Research. So at one point the person in charge of introducing biometric ID cards and one of his main opponents were both miedically unable to provide said biometrics.