The patient is exhibiting the classic symptoms of occlusion of the central retinal artery. The drug of choice for this condition is acetazolamide, which must be administered immediately to prevent permanent blindness. It is contraindicated in hypokalemia, which can occur with use of a potassium-wasting diuretic. The patient is not exhibiting signs of diabetic retinopathy, so asking about diabetes testing is not the most important question. Although the patient has elevated intraocular pressure related to the occlusion, asking about the last intraocular pressure testing is not the most helpful question and would delay treatment. A full vision assessment is important for this patient, however floaters and flashing lights in the field of vision do not change the treatment plan like the presence of hypokalemia; therefore, this is not the most important question.