Bulging Eyes are mostly related to Dropsy - which is water accumulation in the body - but if the body does not show signs of Dropsy then there is a possibility that these Bulging Eyes can be treated, but not in every case.

The problem my be benefited by Salting the water - up to but no more than 7.5% (3/4 ounce per gallon of pond water).

But Bulging Eyes PLUS Dropsy is terminal and there is not a lot that you can do for that fish - by all means try the salt as anything you can do that may help the koi to recover, must be worth a consideration.

Another cause for bulging eyes is stress to the eye for some reason or another, which causes swelling in the choroid (blood vessels behind the eye) and hopefully this will go down in a week or so with the salt treatment in the water.