It's not Hole in the head (HITH), it's Head and Lateral line erosion (HLLE).
"HITH is a parasitic disease found in angelfish and discus. It is caused by Hexamita spp. and/or Sprionucleus vortens and is treated with metronidazole.
HLLE is a nonparasitic condition usually caused by less than ideal food and water quality. This is common in oscars (and many other species). It does NOT respond to any meds, but is treated by improving food and water quality. In some very rare cases it has been demonstrated that the cause in those cases was carbon use in the filter.
Oscars and other larger new world cichlids rarely get HITH, they get HLLE. They key to prevention and or curing is keeping the nitrate concentration below 20ppm(10ppm is better) and feeding a high quality and easily digestable pellet such as New Life Spectrum. Depending on how severe the deterioration of the sensory pits is there may be some permanent scarring but follow the above directions and there will be improvement."
-HUKIT
What are your current water conditions, fish, and tank size?