I've been prescribed prisms by optometrists on my glasses since my teens. Your optometrist can likely do the same and recommend exercises.
My ophthalmologist sent me to an orthoptist a few years ago and I came out with a diagnosis of an ocular nerve palsy for which there's nothing to do beyond what the optometrist is already doing. Two medicals later a new regional medical officer had a panic attack over stability of a condition I've had since my teens
Your prism prescription is correct when you are looking straight ahead without tilting your head when driving on a straight road in the countryside.
You may qualify for a lower category medical and use that to get a private license. Once an experienced pilot, you might qualify for category 1.
Proper fusion is only important in your flare to land. Without you will be either flaring late or early and it will be a long time before you will solo.
Oh yes, some optometrists are more conscientious than others on getting your prisms right.