A 71-year-old woman with non-Hodgkin lymphoma receiving maintenance obinutuzumab (anti-CD20 monoclonal antibody) infusions underwent uneventful pars plana vitrectomy of the right eye for vitreomacular traction. Diluted triamcinolone acetonide (TA) was used to stain the posterior hyaloid. After removal of 25-gauge trocar cannulas, subconjunctival TA and ceftazidime was injected. Owing to cystoid changes in the central macula, a short-acting gas tamponade with sulfur hexafluoride was used to tamponade any cystoid abnormalities that may have been unroofed. Despite unremarkable postoperative day 1 (POD1) examination findings, the patient presented on postoperative week 3 with a painless central scotoma and worsening floaters. Her visual acuity was 20/400 OD and intraocular pressure was normal. There was no external hyperemia or chemosis, and the anterior chamber was deep and quiet with no cells or flare. On dilated fundus examination, there were 15 to 20 cells per high-power field (using a 1 × 1-mm2 high-intensity incidental slit beam) and a white macular lesion with disc edema and scattered intraretinal and peripapillary hemorrhages and mixed venous and arterial sheathing. Optical coherence tomography of the macula showed atrophy, full-thickness hyperreflectivity, and a residual epiretinal membrane (Figure).