A medical emergency is believed to be the cause of an accident in the city of Defiance that left one driver dead.  Defiance Police reports 63 year old Ouida Johnson of Defiance was traveling southbound on Jefferson Avenue at 10:45 Monday morning.  Her vehicle went out of control, striking objects in a yard, and then back into traffic, striking a vehicle operated by 45 year old Maria Rocha of Defiance.  Ouida Johnson was found unresponsive in her auto, and was transported to the Defiance Regional Medical Center by Defiance City Rescue.  She was pronounced dead at the hospital.  Maria Rocha and her passenger, 18 year old Stephanie Gomez-Ruiz of Defiance, were both taken to Mercy Hospital with minor injuries.  Police believe Ouida Johnson was involved in a medical emergency when the crash occurred, leading to her death.  The highway patrol assisted at the scene.