I had ocular migraine(2 weeks ago) half of vision in my left eye was blurred. after it had gone i have permanant reduced acuity in that region causes?

See your doctor: Ocular and neurological migraines can mimic all manner of problems, including those normally caused by strokes. As you describe persistent visual changes, it would be a very good idea to have both an ophthalmologist and a neurologist see you, to make sure nothing else is going on that might need treatment. Please make arrangements to see those doctors soon.

Migraines: Migraines can happen spontaneously without cause. Although there can be triggers, the most common are stress, caffeine, chocolate, red wine, food with sulfates, some medications, alcohol, reflections of light. Typically (never seen it, but has been reported) they resolve completely. You should have an exam by opthalmologist.