Swollen Optic Nerve

[Rosiehippy]

My son aged 12 finally saw an eye specialist this week. His optometrist found he had blue grey halo around his eye. He had special drops put in his eyes to make his pupils big. The eye specialist found he has swelling of his optic nerve in his left eye. My son has been having dizzy spells and blackouts(which now has become total blackouts). He has had trauma to his head, concussions from junior footy(with head gear on), this was on 4 occasions so he now doesn't play footy anymore. His specialist has referred him for a MRI. We just have to wait for the appointment. At first we thought he may have epilepsy which was ruled out via Reg. What would cause this? Wondering if it maybe swelling, bleeding or lesion.
Thanks for your assistance