Can I get an EASA Class 1 medical if I have monocular vision?
The Irish Aviation Authority's aeromedical site directs you to the underlying EU regulations (Part-Med), which say:


  Applicants for a Class 1 medical certificate shall be required to have
  normal fields of vision and normal binocular  function.


That seems to rule out monocular vision completely, which is very strange (to me) considering that the FAA is very clear that binocular vision isn't needed to fly safely. But medical issues are complicated, so I would definitely consult an aviation medical specialist in Ireland before making any decisions.

As for using an FAA medical certificate instead of an EASA one, that should really be a separate question. However, it's highly unlikely to be possible: generally speaking, your pilot's license/certificate and medical have to come from the same country.