Objective: To describe visual acuity outcomes of patients in the Ischemic Optic Neuropathy Decompression Trial (IONDT) after 24 months of follow-up. Design: The IONDT is a single-masked, multicenter, randomized clinical trial. Settings: Patients were evaluated and followed up at 25 clinical centers located throughout the United States. Data were sent to and analyzed at a central coordinating center. Patients: Two hundred fifty-eight patients 50 years or older with nonarteritic anterior ischemic optic neuropathy and visual acuity of 20/64 or worse, but better than no light perception, were randomized to either a careful follow-up group (n= 131) or an optic nerve decompression surgery (ONDS) group (n= 127). Of these, 174 continued participation for at least 24 months, 89 in the careful follow-up group and 85 in the ONDS group. Methods: Randomized patients underwent a standard visual acuity examination at 3, 6, 12, 18, and 24 months of follow- up. The primary outcome was a change of 3 lines or more of visual acuity, defined as a difference of 0.3 in logMAR scores, between baseline and 6 months of follow-up. A secondary outcome was mean change in visual acuity (in logMAR units) at 3, 6, 12, 18, and 24 months following baseline. These changes were estimated using available data from all randomized patients for whom we had data. Results: Of the 258 patients randomized, 143 (55.4%) were male, and 169 (65.5%) were 65 years or older. Mean visual acuity was statistically significantly improved from baseline value at all study visits and for both treatment groups, although visual acuity declined gradually in both groups after the 3-month visit. There were no significant differences between careful follow-up and ONDS in mean change in vision from the baseline and any follow-up time point. At 24 months of follow-up, 31.0% of patients in the careful follow-up group and 29.4% of patients in the ONDS group experienced an increase of 3 or more lines of vision compared with baseline acuity; 21.8% of patients in the careful follow-up group and 20.0% of patients in the ONDS group experienced a decrease of 3 or more lines. In patients who could read at least 1 letter on the Lighthouse chart, there was a gradual decline in mean visual acuity noted over time for both treatment groups, although acuity remained significantly better than at baseline. Conclusion: Analysis of visual acuity data from patients enrolled in the IONDT at 24 months of follow-up confirms that there is no benefit of ONDS compared with careful follow-up in patients with nonarteritic anterior ischemic optic neuropathy.