To establish the safety of an intracameral injection of self-preserved moxifloxacin at the conclusion of routine cataract surgery for the prophylaxis of endophthalmitis and to assess the effect on macular thickness using optical coherence tomography (OCT). Private practice, Bettendorf, Iowa, USA. A retrospective review of the charts of consecutive cataract procedures was conducted to compare outcome measures in patients with or without intracameral injection of moxifloxacin that was diluted to a 0.1% solution in a 100 microg/0.1 mL dose at the conclusion of cataract surgery. In addition, in a prospective manner, macular thickness was measured by OCT in 31 eyes before and 6 weeks after cataract surgery in patients who received the intracameral injection. Aqueous cell counts 1 day postoperatively were significantly lower in the moxifloxacin-treated group (P=.0007). At 1 week, there was no difference between the 2 treatment groups in the number of patients who had no or trace cells. No stromal edema was observed in the moxifloxacin-treated group. Optical coherence tomography studies showed mean increases of less than 3% in macular thickness in all sectors and less than 4% in macular volume at all locations. No drug-related adverse effects were reported. No untoward effects were observed after intracameral injection of moxifloxacin 0.5% ophthalmic solution diluted to a 0.1% concentration at the conclusion of routine cataract surgery.