Hello and welcome - perhaps your fiance is related to Sir Robert Graves, an Irish physician who was one of the early researchers to describe the signs and symptoms of Graves' disease!
Surgery corrects the *hyperthyroidism* due to Graves' disease, but does not cure the underlying autoimmune issue, which is why you can still have eye issues after thyroidectomy.
Your ophthalmologist will likely run a number of simple tests to check your vision and assess how well your eye muscles are moving. He or she might also order a CT scan. This is a great overview of thyroid eye disease from University of Michigan Kellogg Eye Centerhttps://www.umkelloggeye.org/conditions-treatments/thyroid-eye-disease
Loss of vision is very, very rare these days with Graves'. If there is compression of the optic nerve, emergency decompression surgery can save your vision. (Changes in how you see colors are an early warning sign - for example something red like a Coke can starts to look more brown.)
Hopefully, you have a followup with your doctor within a few weeks of adjusting the dose of levothyroxine. Being hyper or hypo is a risk factor for thyroid eye disease. The other thing you can do on your own is to avoid smoking and second-hand smoke.
Wishing you all the best!