To help keep target and front sight in focus as much as possible during practice/learning, practice in very bright conditions. This will cause your pupils to constrict, which increases your depth perception. This is why pin hole cameras don't need focusing lenses.
One possible drill I've read for training eyes somewhere is to use both eyes, then close desired non-dominant eye concentrating on the single eye sight picture then reopen eye trying to focus your mind on the sight image you want from the desired dominant eye. Repeat ad nauseum.
This is an attempting to teach your brain to ignore the sight perspective you don't want while still able to use the eye for peripheral vision. (Note: I didn't need to do this so I can't attest to the effectiveness, though I imagine it would take a great deal of dedication and effort. You are basically trying to reprogram how your brain processes visual information in a single circumstance (shooting) while the brain has years of pre-existing training. Remember it's all a software problem.)