An bhfuil sé fear na leathchluas anois? I was told that when you normally have two organs or appendages, losing one means you express it as half of what we English speakers consider singular. Bó na Leathadhairce - cow with a half horn is one horned (and so is a poitín still). Leathshúil is one-eyed.
I note that aonsúileach is also used for "one-eyed".
Also, you'd use the copula to ask "is he a one-eyed man now?" - An fear leathchluasach é anois?