What is diagnosis for optic nerve thinning?

Possible glaucoma: You would not know about this unless your eye was evaluated by a doctor .. Optic nerve thinning, also termed cupping, can be due to elevated pressure inside the eye which is termed glaucoma. I assume the doctor who discovered this was an ophthalmologist (I hope) who would initiate a work up to see if this is the cause. You should be seeing, for this, an ophthalmologist.