My left eye droops, and diagnosed as myasthenia gravis, but still droops on mestinon (pyridostigmine)?

Possible: First thing we need to know, how certain is the diagnosis? Was it established by blood tests, tensilon test, biopsy? If diagnosis is assuredly myesthenia gravis (mg), it is still possible for the ocular symptoms (droopy lid, double vision) to fail to respond to mestinon (pyridostigmine). See a specialist eye md (neuro-ophthalmologist) to decide if a higher dose of mestinon (pyridostigmine), steroids, or thymus surgery may help.