In a preliminary, open-label pilot study of patients with chronic, steroid-unresponsive ON, Drs. van Engelen, Hommes, and colleagues suggested that improvement in visual recovery could be seen following IgG treatment in patients with chronic, stable ON. These encouraging but preliminary basic and clinical studies have prompted us to design a double-blind and placebo-controlled clinical trial of IVIg in patients with recently acquired but apparently permanent muscle paralysis from MS (NS31506) and to develop this NEI-funded ON study (U10EY1096301).