Cloudy eye(s) can be due to (1) injury (2) infection (3) diet (4) shedding problem (5) exposure to toxin. For diet or toxin, the effect would usually be in both eyes, but not always. It's difficult to say what the cause may be. If it is an infection, it is not easy to treat an internal infection.
Since the newt is still eating and appears healthy otherwise, I wouldn't worry too much. I think you just have to wait and see what happens.