Horse with scratched eye?

My mother in law has a horse that scratched his eye. It became swollen so she had the vet come out. The vet drew blood from the horse and saved 6 tubes of it. She then directed my mother in law to syringe the plasma out and drop that in his eye! This seems very strange to me and cost hundreds of dollars. The vet wanted to hospitalize the horse but since mother in law is on acation she can do the eye drops every hour. I have owned horses my entire life and never heard of this procedure. If a horse gets an eye infection you usually put in antibiotic drops a few times a day, but nothing so drastic as this vet's technique. Anyone else heard of this? do you think the vet is just out for more money?