Currently there is no licensing requrement for non-Pilot helicopter Aircrew. Therefore there is no medical requirement specified. However, individual operators are required to follow industry standard procedures for employee care etc. So its pretty much what the employer dictates to be the standard. I cannot speak for other companies but the one I am involved with requires evidence of physical fitness in the sense that the employment will not make worse or cause any problems. With regard to eyesight, 'Aided' eyesight is accepted and a yearly test is required. CB can be categorised into specific failures.
Having said that, in my companies case, they insist on good vision with allowances made for normal deterioration as a consequence of age etc.
Most Aircrewman type functions seem to be filled by ex service personel who have a valid history of experience/mil training. Ab initio training for a vacant position is not a cost viable option. IMO