This has traditionally been defined as an occludable angle on gonioscopy, a flat iris plane and a relatively deep anterior chamber. It is difficult to diagnose on gonioscopy, however, and is often invoked in patients with acute glaucoma whose intraocular pressure fails to decrease after Yag laser iridotomy. Ultrasound biomicroscopy (UBM) enables clear visualisation of the angle structures and has increased our understanding of the angle closure glaucoma. Using UBM, plateau iris can now be defined by the presence of an anteriorly directed ciliary body, a flat central iris plane, a steep angle between the iris plane and iris root, an absent ciliary sulcus and irido-angle touch. It is most commonly seen in the superior and inferior quadrants of the eye and is found in about a third of Chinese patients with angle closure glaucoma after Yag laser iridotomy (Kumar et al. Ophthalmology 2008).