Thank you for explaining this to both myself and my son. There is no family history so this took a big worry out of our lives ;)
Exo means turns OUT phoria means controled by the fusion reflex (a latent deviation). It becomes apparent or manifest when fusion is disrupted as by doing alternate cover tests.
Exotrophia means the eye is turned out all the time "wall eyes".
Most exophoria is benign, does not require treatment or cause any problem. I'm an eye surgeon and I have exophoria.
It is not the same as "intermittent exotrophia" where sometimes the eyes are straight and sometimes they turn out.
If there is no family history of strabismus or eye muscle surgery the prognosis is excellent.
JCH III MD Eye MD = Opnhthalmologist