A 25-year-old myopic man notices a brown pigmented arc on the corneal endothelium (Krukenberg spindle) and heavy trabecular pigmentation on gonioscopy. He experiences exercise-induced blurring. The mechanism of elevated IOP in this condition is:

• A Pupil block by a swollen lens
• B Inflammatory obstruction of Schlemm's canal
• C Neovascularisation of the trabecular meshwork
• D Reverse pupil block causing iris concavity and mechanical scraping of zonular pigment ✓

Explanation

Pigmentary glaucoma is caused by reverse pupil block in which the posterior iris surface bows posteriorly (iris concavity), rubbing against the anterior zonular packets during eye movements or accommodation (particularly exercise). This mechanical friction liberates pigment granules, which accumulate in the trabecular meshwork and impair aqueous drainage. Krukenberg spindle (vertical pigment on corneal endothelium due to aqueous convection currents) and Sampaolesi line on gonioscopy are characteristic findings.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.