It seems in UK there's need to apply for
$1 and be "registered" as severe partially sighted or blind/"legally blind". Under that link it seems the procedure how it's all done to check if you're eligible good described.
Ask your eye doctor. Generally it has to be separate applied in some special forms to special institutions and they will check you if person is disabled or not it's not automatic and you can't just mark in forms you're disabled if you don't have certificate/proof etc just a note from your doctor or your words won't be enough.