Statistics regarding improvements in vision following eye muscle surgery are not impressive. However, success was defined as ANY long-lasting positive benefit.
Many surgeons recommend surgery for cosmetic purposes only.
It is extremely important that your surgeon be explicit about the goals for any surgery recommended. Ask what results can be expected. The surgeon should be very clear as to whether multiple surgeries might be recommended. After every previous surgery her eyes had eventually reverted to the crossed position. Age has an impact on whether surgery is appropriate.