The IONDT is the first multicenter, prospective study of newly diagnosed patients with NAION. The baseline history and examination, which took place within 14 days of the onset of symptoms, used standardized methods and diagnostic criteria to collect data on all factors possibly relating to the etiology of NAION. In reports from previous studies that present data on both initial and final visual acuities, no data are available regarding change in visual acuity over time for individual patients. Where data are available on final visual acuity, reported rates of improvement are low, ranging from 0 percent to 33 percent for untreated eyes. The IONDT found, however, an improvement of three or more lines in 42.7 percent of patients who received careful followup.