Hi,
My name is S. and I have a 38 year old son who was born with Duane syndrome. He too looked a little cross-eyed, especially when he tried to look to the left. As I understand the syndrome, one of the 6 tissues in his eyes never developed into a muscle, so the tissue just remained a tissue and kept his left eye from turning to the left. It could go right, though. When he was 3, the doctor went ahead a operated to allow the tissue to loosen somewhat so that my son's eye was able to look a little straighter and be in a left position a little more, so he did not look quite so cross-eyed.
All my son ever wanted to do was to be a jet pilot. Needless to say, this syndrome elminates his periferal vision on the left...so he could not even enlist in the service, let alone get a license to fly.
The good news is that he has never even needed to wear glasses. He does have somewhat of a "lazy eye," which apparently is normal for this condition, but he drives and does NOT need to wear eye glasses as a condition of driving a car.
My concern as a mother was only that he could get hurt by playing a sport that would make him vulnerable because he had no peripheral vision on his left side. Other than that, I don't think Duane's Syndrome really limited him beyond keeping him from the career that was one that he had always wanted... and that was primarily because both of his grandfathers and 2 of his uncles were jet pilots. Even if that were the case, there are many wonderful career choices and opportunites in life that offer your child a great life, so I truly wouldn't worry. I would explore the operation, though, if you've not done so already. Good luck!
PS
I read a note below about eye therapy and what I'm thinking the person is advocating is exercise. As I'm sure your doctor already told you, the issue with Duane Syndrome is that the tissue never developed into muscle so there's nothing to exercise. You can only loosen the tissue, you can't turn it into a muscle.