Correct.. there will always be some roundness to their eyes when looking from above- but as shown in the picture, there will be an extremeness to them if they have come down with popeye.
Popeye isn't necessarily deadly itself, but if not treated quick enough can lead to loss of the eye. Sometimes popeye is a symptom of other ailments such as dropsy, which is deadly.. so you would have to look for other symptoms to see whether or not a fish has just a case of popeye, or something more severe.
The one posted above me is a bulging eye.
In the first picture you will see the eyes are proportionate to the head.. that one is a healthy eye.
The one on the right here is a cloudy eye with some bulging.