Dry, sore area on ears & scabs above eyes

[F4kehistory]

New here but wondered if anyone had any advice. Hogarth has been to the vets for suspected flea allergy. Vet game him flea treatment, antibiotic and steroid injections but these don't seem to have worked as it's been 2 weeks and his symptoms are just worsening again. He had fleas before and didn't have a reaction to them so I don't think it's that (also haven't seen any fleas and he is an indoor cat, only pet we have).
He has sore ears, the fur is going and they look very dry and cracked. He has a scab about the size of my finger nail on the top of his head, and he has scabs on his brow bone on both sides.

[Kay]

These areas are typical of skin irritation from a food allergy - if you look at the images on Google under food allergy cats you'll get an idea

What do you feed him on?