There was an interesting study on the middle ear volume, and it ended up being about 1.4 ml in non diseased individuals. In reality, you rarely get a full ml of fluid into the middle ear when you inject it. There is a number of reasons we put medications directly into the middle ear, such as Meneir’s Disease, sudden sensorineural hearing loss, etc… We are typically using an anti inflammatory such as dexamethasone or an ablative medication such as Gentamycin. Sometimes we combine the agents. When I use the Dexamethasone, I do no dilute, and I put in as much as the middle ear will handle. I typically anesthetize the ear with phenol or EMLA and have patient stay laying in the injection position without swallowing for 20 minutes if possible.