Hole in the head is a disease of tropical fish which starts with smalls sore on the head above the eyes. These sore grow and eventually penetrate through the outer layer of skin.
Hole in the Head is most often seen in large Cichlids or other large fish. Oscars are large Cichlids and are often infected with Hole in the Head.
It is also the result of poor water quality over a long period of time. It's best to prevent Hole in the Head by doing the proper maintenance schedule. Usually it occurs in aquariums with under-gravel filters, and sometimes in aquariums with canister filters, but rarely in aquariums with a BIO-Wheel filters. To treat HITH you should immediately begin the recommended Maintenance Schedule and get the properly size aquarium filter with a BIO-Wheel. Then begin cleaning your gravel with a gravel washer. When the gravel is clean, remove most of it and remove the undergravel filter. Since you have an Oscar be sure it has a large enough aquarium. One large Oscar 8-inches in length needs at least 80-gallons of water. Two 8-inch Oscars need at least 150-gallons of water. More Oscars and larger Oscars need even bigger aquariums with more water. However, the Recommended Treatment usually will not cure Hole in the Head. It's worth a try, and it may work, or it may arrest the disease, so the fish can survive. p.s just raise temp and add salt.
Hope this helped.