A 32-year-old man presents with a 3-day history of pain, photophobia, and blurred vision in the right eye. On examination, the anterior chamber shows 2+ cells and flare with fibrin, and a posterior synechiae is noted. Intraocular pressure is 18 mmHg. Fundus examination is normal. There is no systemic history of concern. What is the most appropriate immediate next step in management?