Background and Objective: Optical coherence tomography (OCT) was used to evaluate the macular thickness in eyes with advanced glaucoma compared with eyes following a retinal artery occlusion. Patients and Methods: Ten patients with a retinal artery occlusion and 10 patients with severe glaucoma were evaluated with OCT using the macular thickness map protocol. Results: The median thinnest macular sector was 183 microns (range: 152 to 223 microns) in patients with glaucoma versus 143 microns (range: 98 to 177 microns) in patients with arterial occlusion ( P = .001). Median macular volume was 5.9 mm 3 (range: 5.1 to 6.7 mm 3 ) in patients with glaucoma versus 5.1 mm 3 (range: 3.6 to 6.1 mm 3 ) in patients with arterial occlusion ( P = .015). Conclusions OCT demonstrates that patients with a retinal artery occlusion have significantly reduced macular thickness compared with those with severe glaucoma. [Ophthalmic Surg Lasers Imaging 2007;38:392–398.]