Neuroophthalmologic effects of intravenous magnesium sulfate. To test the hypothesis that visual disturbances are more common during intravenous magnesium sulfate administration than at 1 to 4 days after discontinuation of the drug, 13 women underwent bedside neuroophthalmologic examinations during intravenous magnesium sulfate tocolysis at 2.0 to 3.0 gm hr and again at 1 to 4 days after cessation of therapy. Visual symptoms were common during intravenous magnesium sulfate administration. Blurred vision was present in 12 of 13 patients and diplopia was present in 10 of 13 patients. Abnormal findings during neuroophthalmologic examination occurred in all patients during intravenous magnesium sulfate administration. Findings included ptosis, accommodative and convergence insufficiency, and abnormal pupillary responsiveness to light and near. All patients were symptom-free and had normal examinations after magnesium sulfate was discontinued. These findings suggest that visual disturbances with therapeutic magnesium sulfate are common. 