study finding that over 60% of treated Chinese eyes were still manifesting post-iridotomy irido-trabecular contact, requiring continued glaucoma management.69 Moreover, after receiving a patent

laser iridotomy for an acute attack, some eyes experience repeated acute angle-closure attacks.70,71 Thus it appears that the effective-

ness of laser intervention may not always be either benign or curative; its effectiveness appears to be stage-specific to the disease, and dependent on underlying mechanisms other than pupillary block.

Consider the implications of the high rates of PACG found in surveys of select Chinese and Indian populations, affecting nearly 2% of individuals over the age of 40 years old: with nearly half of the

world’s population living in India and China, scores of millions of people potentially require iridotomy.22,31,36,72 Because of the major

public health ramifications in this context of millions of potentially affected eyes, it is imperative to determine whether laser iridotomy treatment induces even a small percentage of vision impairment when utilized prophylactically. Even a fraction of a per cent of postiridotomy complications of cataract or corneal changes would affect enormous numbers of people with limited access to address their vision loss. Further research as to the benefits and demerits of each approach – either to recruit eyes with the earliest stigmata for consideration of treatment, or to reach a predetermined threshold or stagespecific criterion before progression – remains to be determined.

The end condition of primary angle-closure glaucoma includes the fundamental criteria for any glaucoma: damage to the optic nerve, with concomitant loss of visual field function. Hence the screening strategies for epidemiologically detecting this advanced stage of PACG are identical to those efforts for detecting primary openangle glaucoma: optic nerve evaluation and, when feasible, perimetric assessment. In circumstances where advanced PACG disease with compromised media prohibits disc and visual field testing, for example cataract or corneal disease, a coarser definition holds for PACG whereby an IOP 24 and/or acuity of 3/60 (20/400), or a history of prior glaucoma surgery, will suffice.The stigmata of prior angle-closure attacks other than PAS – such as glaucomfleken changes in the anterior lens, patches of iris necrosis, etc. – are worth noting, but are not in themselves predictive.25

Presentations of primary angle-closure disease

The manifest advantage of the simple tripartite definition of PAC disease, based solely on the findings present at the time of the exam, is essential for epidemiologic and comparative studies. But

for deciding management and follow-up options, the clinician too must determine whether the presenting eye is a PAC suspect, manifests closure, or has PACG itself.This is the first step of management. Next she must then methodically distinguish among a variety of anatomical pathophysiologic mechanisms at play in the presenting eye. Hence a mechanism-based scheme complements the diagnostic definitions; together they illuminate the natural history and stage-appropriate findings which require intervention.

New imaging technologies

As with optic nerve imaging,technological advances have profoundly impacted our understanding of patterns of anatomic alterations underlying angle-closure disease. There are two major devices whose contributions dominate the current clinical literature:

1.Ultrasonic biomicroscopy (UBM)73 requires a skilled technician, a supine patient, and a water-bath coupling probe on the eye. With tissue penetration of 4 mm, a UBM’s resolution typically includes angle structures as well as imaging of the anterior lens and anterior ciliary processes; images appear as radial slices of one portion of the angle. Because UBM scans are obtained in

real time on video, there are resultant advantages (e.g., dynamic capture of anterior segment responses to accommodation, or to dark or light stimulation, etc.) (Fig. 15-3) and disadvantages (e.g., relatively low-resolution images, movement artifact, etc.)

2.Anterior segment ocular coherent tomography (AS-OCT) uses infrared light while examining a sitting patient without direct ocular contact; single-frame pictures can be obtained under different lighting conditions. Images comprise a 180°-diameter slice of the anterior segment (Fig. 15-4), currently limited to but a few clock hours (e.g., 3–9 o’clock scan), but dramatically capture the pupil and iris–trabecular configuration in high definition.The limited penetration of the light source restricts resolution to the angles and iris only, without reliable imaging of the anterior ciliary processes or lens. Nevertheless, highly detailed calculations of such parameters as angle opening distance, angle recess area, and the trabecular–iris space area

introduce new levels of precision for approaching PAC disease.74,75

Both kinds of instruments propel investigations of subtle changes heretofore invisible to earlier investigators:76–98 correlation of gonioscopy and measurable parameters in imaging of the angle;99 alterations in angle configuration from laser iridotomies or cataract