Hidden mechanisms beyond the pupillary block in acute angle closure: ultrasound biomicroscopic study

BackgroundTo evaluate the mechanisms of acute angle closure (AAC) other than the pupillary block using ultrasound biomicroscopy. DesignRetrospective chart review. ParticipantsAll patients who were diagnosed with AAC in Ramathibodi Hospital, Bangkok, Thailand, between June 2011 and February 2015 were enrolled. MethodsSeventy-two patients who were diagnosed with AAC underwent a detailed ocular examination. The diagnosed mechanism of AAC was confirmed by UBM and ocular biometry. Main Outcome MeasuresPrimary mechanism responsible for acute angle closure. ResultsIn 72 patients, the mean age was 62.3310.4years, 18 (25%) patients were male and 54 (75%) patients were female. The primary mechanism of AAC was iridolenticular wrapping (crowded-angle (CR) plus anterior lens subluxation (LS)) in 49 eyes (68.1%), pupillary block (PB) in 17 (23.6%) eyes, and plateau iris (PL) in 6 (8.3%) eyes. Thirty (41.7%) out of 72 eyes without previous iridotomy before UBM examination were analyzed. The most common primary mechanism in this group was iridolenticular wrapping (20 eyes, 66.7%). There were seven (23.3%) eyes that had a pupillary block, and only three (10.0%) eyes had plateau iris syndrome as the primary mechanism of AAC. There was a single mechanism in 14 (46.7%) eyes, and there were combined mechanisms in 16 (53.3%) eyes. ConclusionsThe most common mechanism contributing to AAC development in this Thai population was iridolenticular wrapping. From this study, we suggest that iridolenticular wrapping was the most common hidden mechanism beyond pupillary block among Thai patients.