Rosh Emergency Medicine Practice Test

In a patient presenting with acute right eye pain and a mid-dilated nonreactive pupil, what is the pathophysiology behind the most likely diagnosis?

1. Decreased drainage of aqueous humor via trabecular meshwork

2. Inflammatory demyelination of the optic nerve

3. Lens opacification due to age-related degeneration

4. Obstruction of the central retinal artery due to emboli

The correct answer is: Decreased drainage of aqueous humor via trabecular meshwork

The scenario described – acute right eye pain accompanied by a mid-dilated nonreactive pupil – is suggestive of acute glaucoma, particularly angle-closure glaucoma. In this condition, there is a sudden increase in intraocular pressure due to the obstruction of aqueous humor drainage. The correct answer highlights the pathophysiology of decreased drainage of aqueous humor via the trabecular meshwork. In a normal eye, aqueous humor is produced by the ciliary body, flows through the anterior chamber, and drains via the trabecular meshwork into Schlemm's canal. In angle-closure glaucoma, the anatomical configuration (often due to a shallow anterior chamber) leads to closure of the angle between the iris and the cornea, which in turn impedes the flow of aqueous humor out of the eye. This obstruction results in an increase in intraocular pressure, causing pain and altering pupil responsiveness. The mid-dilated nonreactive pupil is a direct consequence of the increased intraocular pressure and the effects on the iris and pupil muscles, which can lead to a fixed posture. This characteristic presentation is critical for distinguishing angle-closure glaucoma from other possible ocular pathologies.