A sphenoidal meningioma enplaque is a difficult condition to treat, even with all advancements in medical technology. The treatment depends on the extent of the meningioma, specially if it is also involving the right optic nerve, partially.
Apart from surgery, the other treatment for meningioma is radiation therapy or radiotherapy. Radiotherapy carries the risk of damaging structures around the tumour also, hence, the other optic nerve may be at risk. Meningioma grows very slowly, hence it can be observed for a long period of time. There are no medicines to treat a meningioma. I would suggest a conference between your neurosurgeon and neuro-ophthalmologist.