A 35-year-old woman presents to a hospital ward from an urgent care clinic with a 5-day history of progressive left eye swelling and severe pain. She reports worsening diplopia, particularly with upward gaze, and significant discomfort when attempting to move her eye. For the past week, she has also experienced a persistent, purulent nasal discharge and frontal headache. On admission, her vital signs are: blood pressure 132/80 mm Hg, pulse 92/min, respiratory rate 16/min, temperature 38.8 C (101.8 F), and oxygen saturation 97% on room air. Physical examination reveals marked periorbital edema, erythema, and tenderness of the left eyelid. There is notable proptosis of the left globe, and extraocular movements are severely restricted, particularly adduction and supraduction, causing intense pain. Pupillary reactions are normal, and fundoscopy is unremarkable. The right eye appears unaffected. Given these clinical findings, what is the most likely diagnosis and the immediate course of management?

A 35-year-old man presents to an urgent care center complaining of progressive left eye pain, redness, and swelling over the past 3 days. He also reports a greenish discharge and headache. His medical history includes type 1 diabetes mellitus, well-controlled with insulin. On arrival, his temperature is 39.2°C, blood pressure is 130/75 mmHg, pulse is 105/min, and respirations are 18/min. Oxygen saturation is 97% on room air. Physical examination of the left eye reveals significant periorbital erythema, marked edema, and proptosis. Ocular motility testing demonstrates painful restriction of extraocular movements in all gazes, and there is a noticeable decrease in visual acuity in the affected eye. Pupillary responses are sluggish. Which of the following is the most likely diagnosis and the most appropriate initial management strategy?

A 45-year-old woman presents to a general hospital ward with a several-day history of worsening pain and swelling around her left eye. She reports that the vision in her left eye has become increasingly blurry and she is now experiencing persistent double vision. Her medical history is notable for chronic sinusitis and a distant history of intravenous drug use. Current medications include intranasal fluticasone for her sinusitis. On examination, her temperature is 38.2°C (100.8°F), blood pressure is 118/72 mmHg, pulse is 105 beats/min, respirations are 16 breaths/min, and oxygen saturation is 97% on room air. Physical examination of the left eye reveals significant periorbital erythema and edema, proptosis, and marked pain upon attempted extraocular movements in all directions. Her left pupil is reactive but visual acuity is reduced to counting fingers. There is no discharge or vesicles noted. Laboratory results are pending. Considering the patient's presentation, what is the most appropriate initial management strategy, and what potential serious complication should be closely monitored?