Nystagmus intensities at various gaze angles were studied both preoperatively and postoperatively, using accurate ocular motility recordings, in three cases of congenital nystagmus. In addition to shifting the nystagmus null, the surgery broadened the null region and resulted in an overall reduction in nystagmus intensity at all gaze angles. Surgical rotation also resulted in improved visual acuity in all cases. The postoperative acuity at 0 degrees was better than the preoperative acuity at both 0 degrees and the patient's preferred gaze angle (ie, the preoperative null angle). This was not only for the two patients who showed an improved preoperative acuity with their head turn but also for the patient whose preoperative acuity did not substantially improve with her preferred head turn. Eye movement recordings have made it possible to accurately determine the amount of surgery required and to predict acuity increases even when undetectable during the preoperative clinical examination.