A 55-year-old woman with a narrow angle is found to have plateau iris syndrome on ultrasound biomicroscopy (UBM) after a laser peripheral iridotomy has already been performed. The UBM finding that confirms plateau iris (rather than residual pupil block) is:
- A Anteriorly positioned ciliary body with forward rotation, causing peripheral iris to be pushed anteriorly against the trabecular meshwork ✓
- B Posterior iris bowing with concave iris contour on UBM
- C Iridodonesis with posterior capsule attachment to the iris
- D Large crystalline lens with anterior displacement
Explanation
Plateau iris syndrome is caused by an anteriorly positioned and anteriorly rotated ciliary body that holds the peripheral iris flat against the drainage angle even after successful PI has opened the pupil block. On UBM, the pathognomonic finding is the 'double hump sign' — a central shallow anterior chamber (from normal anterior aqueous dynamics post-PI) with peripheral iris apposition to the trabecular meshwork due to the anteriorly positioned ciliary processes. The iris typically shows a flat rather than bowed contour. Lens-iris contact causing posterior bowing is the UBM finding in pupil block.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.