A 58-year-old woman presents to the emergency department with acute onset of severe eye pain, blurred vision, and halos around lights in her right eye for the past 6 hours. On examination, the cornea is hazy, the pupil is mid-dilated and fixed, and intraocular pressure is 52 mmHg. Clinical suspicion for acute angle-closure glaucoma is high. Which investigation is most appropriate to confirm the diagnosis and assess the fellow eye?