Do you think amblyopia treatment would yield any results if it starts at the age of 18 years?

Unlikely: The brain is wired in such a way as to allow some improvement from amblyopia if treated early (before age 7). After age 9, there is little that can be done to reverse amblyopia, although intense therapy may recover a small amount of vision.

No: Unfortunately, if amblyopia (or lazy eye) is not diagnosed until your late teens, treatment will not help significantly to improve the vision in that eye. Amblyopia should be diagnosed in early childhood if possible. The younger the child is when he starts treatment (usually patching of the good eye) the better chance he will have to improve that eye.