Double vision looking to the far left only for ten years. Is it hopeless or serious?

When this double vision thing began years ago I thought it was simply because I was tired and older. But for some unknown reason it has me concerned lately . Two years ago an optometrist said I didn’t even need glasses. What caused it and what will the opthamologist do? Or, I should say, what will I allow him to do. It is only to the far left-so far.