Generic Drugs

Lately I have found treating Glaucoma to be very frustrating.  More and more of our drugs are being pushed as generics, yet they are clearly not equivalent drugs.  Every drug company has numerous studies showing the subtleties of ophthalmic drug formulation, from preservatives to suspension size, that have dramatic effects on the effectiveness of drugs via the topical ophthalmic delivery route.  Yet when we petition to have a more effective drug approved for our patients, we are asked on a case by case basis to 'prove' that the generic is not effective.  Excuse me?  How about we have the generic manufacture 'prove' that it is?  How exactly do I 'prove' the drug was ineffective in clinical practice?  To further muddy the water, numerous manufactures are making the same drug with differing formulations, and patients receive these different bottles at random.
Someone needs to find out!