Deconstructing the mechanisms of angle closure with anterior segment optical coherence tomography.

BACKGROUND: To illustrate the common mechanisms of angle closure by observing the changes following a laser iridotomy and then cataract surgery with anterior segment optical coherence tomography.
DESIGN: Retrospective interventional case series. PARTICIPANTS: Four patients with iridotrabecular contact.
METHODS: The anterior chamber was imaged in different lighting conditions prior to and following a laser iridotomy and then cataract surgery. The images were superimposed on each other, using the interscleral spur line as a common baseline. MAIN OUTCOME MEASURES: Qualitative and quantitative analysis of the changes of the iris and the drainage angle.
RESULTS: Iridotrabecular contact was seen in dark conditions in all patients. Iridotrabecular contact related to pupil block was abolished after a laser iridotomy. Persistent iridotrabecular contact following a laser iridotomy, due to a lens-induced mechanism, was abolished after cataract surgery. Iridotrabecular contact that persisted after a laser iridotomy and cataract surgery was due to a 'pure' plateau iris syndrome or peripheral anterior synechiae. These treatments lowered the height of the iris plane in the region posterior to the trabecular meshwork.
CONCLUSION: Following a laser iridotomy and cataract surgery, there is posterior movement of the iris plane away from the trabecular meshwork, but iridotrabecular contact can persist due to the ciliary processes or peripheral anterior synechiae. These changes show that the risk of iridotrabecular contact depends on the height of the iris plane relative to the trabecular meshwork and the degree of physiologic pupil dilation, and that angle closure can be a multi-mechanism disease rather than a pure one.