A 42-year-old woman presents to the emergency department with a 24-hour history of severe pain...

The most likely diagnosis is acute anterior uveitis (iritis). The key MCCQE clinical pattern is painful red eye with ciliary flush (injection worst adjacent to the iris/limbus) and marked photophobia, especially consensual photophobia, which strongly points to inflammation of the iris and ciliary body. The sluggish light response and miosis (smaller pupil) are also typical of iritis due to sphincter spasm and inflammation. Intraocular pressure is normal, helping to rule out acute angle-closure glaucoma, which usually presents with elevated IOP, corneal haze, and a mid-dilated fixed pupil. Optic neuritis classically causes decreased color vision and pain with eye movement rather than ciliary flush. Viral conjunctivitis causes diffuse conjunctival injection and irritation/grittiness, not severe pain with consensual photophobia. Scleritis causes deep “boring” pain and violaceous scleral hue, not miosis/consensual photophobia as dominant features. Difficulty visualizing the fundus can occur with significant miosis.