Angle-closure glaucomas (ACGs) are situations of elevated IOP caused by the physical obstruction of the anterior chamber angle (trabecular meshwork and ciliary body face). When presented with a case of suspected ACG, it is critical to differentiate the various conditions, because their treatment differs. While considering the differential diagnosis (Table 1), you may find it helpful to stratify the various conditions by underlying mechanism and the presence of symptoms.
DIAGNOSTIC WORKUP
History
Symptoms such as pain, seeing halos around lights,
and the rapid occurrence of conjunctival hyperemia/injection suggest a rapid change in IOP resulting in
corneal edema. In contrast, a gradual elevation of IOP
allows the cornea to compensate and not become
edematous. Eyes with chronic-onset ACGs can have a
surprisingly high IOP but a clear cornea and no symptoms
save vision loss due to significant optic nerve and
visual field damage.
Question patients regarding pertinent risk factors for the secondary ACGs such as a past medical history of diabetes or uveitis, recent changes in medication, recent ophthalmic surgery, etc.
Office Examination
The presence of a shallow anterior chamber can be
inferred from the shadow cast on the nasal iris from a
light held temporal and roughly parallel to the plane
of the limbus—otherwise known as the flashlight test
(Figure 1). On slit-lamp examination, many diagnostic
aspects for the various etiologies of both primary and
secondary forms of angle closure are visible (Table 2).
Gonioscopy is diagnostic for ACGs. With pupillary block acute ACG or its precursor condition (or anatomic configuration), the angle structures may not be visible except with indentation gonioscopy (Figure 2). Gonioscopy is the only way to clinically diagnose plateau iris syndrome. A prominent last iris roll is visible that moves poorly during indentation gonioscopy (Figure 3).
In chronic angle closure, angle structures will not be visible for the majority of the angle, and there will be peripheral anterior synechial adhesion from the chronic apposition of the peripheral iris to the trabecular meshwork. In secondary cases, peripheral anterior synechial adhesion will be significant, either from the contraction of a membrane that has grown over the angle (eg, neovascular, iridocorneal endothelial syndrome) or iridocorneal adhesions to areas of abnormality (posterior polymorphous dystrophy, adhesions to defects in endothelial or Descemet membrane thickening, uveitis, adhesions to keratic precipitates on the cornea or trabecular meshwork).
In eyes with narrow angles and suspected intermittent angle closure, you may wish to consider provocative testing in a dark room (to induce pupillary dilation) and with the patient in a head-down (ie, prone) position so that gravity pulls the iris-lens diaphragm forward to further crowd the angle.
Imaging
Although most forms of ACG can be detected
through history and clinical examination, imaging can facilitate the diagnosis and your monitoring of
some patients. Ultrasound biomicroscopy (UBM) uses
50-MHz ultrasound to provide a tissue resolution of
approximately 50 μm and a tissue penetration of
4 to 5 mm. In contrast, typical B-mode ultrasound uses
between 8 and 15 MHz with a rough resolution of
100 to 120 μm. During UBM, the sound waves penetrate
through the iris to permit
visualization of angle structures,
the ciliary body, and the anterior
pars plana. This is particularly
advantageous for the detection of
pathology of the ciliary body
(eg, swelling, anterior rotation,
anterior positioning, subtle uveal
effusion, etc.; Figure 4) and structures
located in the posterior
chamber (eg, ciliary sulcus).
Anterior segment optical coherence tomography uses coaxial light to provide very high-resolution images of the topography of the anterior segment structures. The technology's main disadvantage is that it does not image structures posterior to the iris well.
Douglas J. Rhee, MD, is an associate professor, Harvard Medical School, and associate chief of clinical operations and practice development at the Massachusetts Eye & Ear Infirmary in Boston. Dr. Rhee may be reached at (617) 573- 3670; douglas_rhee@meei.harvard.edu.
