FCEM2-1379

A 42-year-old woman comes in with a painful, red left eye and sensitivity to light. She also reports seeing floaters and experiencing a dull, throbbing headache. She is currently being evaluated by the rheumatology team for persistent pain and stiffness in her upper back and discomfort in her buttocks and thighs. Her eye appears red, and a hypopyon is visible.

What is the SINGLE most probable UNDERLYING diagnosis?