exophoria is a latent deviation (the eyes are straight when both open and only turn out when one eye covered.
Exotropia or intermittent exotrophia in children is sometimes treated with over-minus lens to try and stimulate fusion and turn exotropia into exophoria.
However it does not work for adults because the focus muscle is so much weaker and gets weaker as we age.
JCH MD
can i advice patient to use mince lens for exophoria even he is normal
I can't tell from your description. You need to see an eye muscle specialist that is a MD physician-ophthalmologist. The way your were treated suggests you saw a non-MD non-physician limited scope eye care provider (optometrist).
You can go to www.aao.org and use the Find An Eye MD feature to locate a strabismus-pediatric ophthalmologist near you (most eye muscles doctors do mostly kids but also adult eye muscle problems).
The longer you wear prism glasses the more dependant you get on them.
JCH III MD