Gonioscopy is an indispensable technique to visualize the angle structures and detect angle closure. It is important to perform gonioscopy in a completely darkened room using the smallest square of light for a slit beam that sets off the pupil because slit-lamp illumination can stimulate pupillary light reflex and widen the angle (Fig. 17-2). A narrow angle is usually defined as an angle in which more than 270 degrees of the posterior trabecular meshwork cannot be seen. Indentation gonioscopy is useful for differentiating synechial closure from appositional closure. Synechial closure is recognized when there are considerable acquired adhesions between the iris and the corneoscleral junction at the angle. Peripheral anterior synechiae may extend circumferentially, resulting in synechial closure and progressive increase in intraocular pressure (Fig. 17-3). The extent of peripheral anterior synechiae correlates with the risk of developing glaucoma.

Although assessment of the angle with gonioscopy is largely qualitative and subjective, objective and reproducible measurement of the anterior chamber angle can be obtained with cross-sectional imaging devices like the ultrasound biomicroscopy (UBM) and the optical coherence tomography (OCT) (Fig. 17-4). OCT has a number of advantages over UBM for anterior chamber angle imaging. It is a noncontact technique, has a higher image resolution, and is more precise in locating the position of interest for evaluation compared with UBM. UBM, however, has a unique role in visualizing the ciliary body. Commercially available time-domain and spectral-domain models have been developed for anterior chamber angle imaging⁵ (Table 17-1). With the development of high-resolution OCT imaging systems, angle structures including the scleral spur, Schwalbe’s line, Schlemm’s canal, and collector channels can be examined in greater detail (Fig. 17-5). High-speed imaging allows evaluation of the angle in 360 degrees. Visualization of the iris profiles and the angle configurations is enhanced with three-dimensional reconstruction (Fig. 17-6). The latest anterior segment swept-source OCT (CASIA II, Tomey, Nagoya, Japan) provides automatic segmentation of the anterior segment structures and quantification of the anterior chamber angle dimensions in 360 degrees (Fig. 17-7). This new feature would improve the detection of primary angle closure. Examination of the anterior chamber angle with OCT and UBM not only augments the diagnostic performance to detect angle closure, but also improves our understanding in the pathophysiology of primary angle closure.