A 58-year-old woman presents to the emergency department with sudden onset of severe left eye pain, blurred vision, and nausea for the past 4 hours. She reports seeing halos around lights. On examination, the left eye shows conjunctival injection, a mid-dilated fixed pupil, corneal edema, and intraocular pressure of 68 mmHg. Gonioscopy reveals a closed angle. The right eye is normal with IOP 14 mmHg and an open angle on gonioscopy. What is the most appropriate immediate management?