Hard to say if there's a problem without seeing the fish. But it isn't uncommon for fish to damage the front, exposed part of the eye during capture and transport. If the damage is slight, they seem to recover. However, there are some unusual parasites that can infest this part of the eye as well, and so far as I know, they're untreatable. I'd tend to assume the fish had been damaged, and take extra care over the next few weeks. Tweaking the salinity a bit could help, particularly if this goby has been mostly kept in freshwater until now. Knight Gobies are notoriously delicate in freshwater aquaria, even though they seem to be as much freshwater fish in the wild as they are brackish water fish.