What Causes Persistent Headache After An Accident?

My son had an accident for a year ago and that caused a bleeding in his eyes ,glaucoma ,angle recession .Now his case becomes stable but with eye drops.Now he suffers from pain at his left and right sides of the head starts with a light pulses untile ends with severe headache He did MRI but it was good.I would like to know what the cause of the headache ,with the knowledge that the accident cused a bit damage at the optic nerve