Figure 3.

Postoperative diplopia test. Adult patient presenting with large angle exotropia and suppression of the deviating eye. (A) Left exotropia of 45 prism diopters as measured with the alternate prism cover test. (B) Postoperative diplopia test being performed preoperatively to determine the risk of potential diplopia if strabismus surgery is performed. With both eyes uncovered, a base-in prism bar is held in front of the deviating eye as increasing prism strength is introduced until either the objective angle of deviation is reached or patient begins to appreciate diplopia.