NBEO Binocular Vision Practice Test

XP denotes an outward, latent misalignment of the eyes, called exophoria. The X signals outward deviation and the P indicates phoria—the tendency to drift that is kept in check by fusion and only reveals itself when binocular fusion is disrupted (for example, during dissociation). This differs from exotropia, which is a manifest outward deviation seen even when both eyes are used together. In contrast, esophoria and esotropia describe inward deviations, latent and manifest respectively. So XP is used for exophoria, not exotropia or the inward forms.