Vergence adaptation maintains heterophoria in normal binocular vision

This investigation sought to determine whether vergence adaptation serves to maintain orthophoria or heterophoria in normal binocular vision. While wearing prisms which neutralized their nearpoint (40 cm) heterophorias, 27 of 30 nonstrabismic subjects adapted from their prismatically created orthophoria toward their habitual heterophoria. Three subjects showed no adaptive response. A symptom questionnaire distributed to these subjects determined that the maintenance of heterophoria by vergence adaptation is: characteristic of normal and comfortable binocular vision, and neither an entirely necessary nor sufficient condition for normal and comfortable binocular vision.