Backbone: the direction of testing/diagnosing and treating a vergence issue is the opposite of that of the eyes’ compensating vergence.
EXO (X) eye looks out.
Diagnosis and Treatment:
– BI prism (I) brings eyes out and eyes compensate with Positive Fusional Vergences (P) to bring eyes more in, relieving (X)
-> DX/TREAT w (I)
Compensate w (P)
– Negative/ Minus lenses (N) stimulate accommodation, drawing the eyes out. This change is compensated with (P) to eventually make eyes move more in, relieving (X).
-> DX/Treatment w (N)
Compensation w (P)
Overall, for (X), you treat/diagnose with (N) or (I) and compensate with (P)to bring eyes more in.
Therefore, NIX (remember P, or positive, as being the opposite as negative, or N, and dx/treatment are the opposite of compensating vergences)
The same logic applies to POS.
For ESO (S), you treat or diagnose the condition with plus or positive (P)lenses and BO prism (O).
The eye compensates with (N) or negative fusional vergences to eventually bring the eyes out more and relieve the (S) symptoms.