Acute angle-closure glaucoma – assessment

Description

Acute angle-closure glaucoma (ACG) is usually characterized by a dramatic, rapid rise in intraocular pressure (IOP), causing a marked threat to vision. The mechanism of ACG is an occlusion of the anterior chamber angle, in which peripheral iris tissue covers the trabecular meshwork, due to either pupillary block or plateau iris syndrome. Risk factors for ACG include a shallow anterior chamber (less than 2 mm deep centrally), which is more common in Asian people, the elderly, women, and those with a thick crystalline lens, hypermetropia or a positive family history. ACG can also be precipitated by pupillary mydriasis in susceptible patients. The risk factors are typically bilateral, the fellow eye having a 75 per cent chance of also developing ACG.

Symptoms

Acute ACG is associated with a red, painful or aching eye, reduced vision, haloes around lights, and even nausea and vomiting. If the condition is subacute, the symptoms may occur in intermittent episodes. In chronic (creeping) ACG, the patient may be asymptomatic despite advanced signs

Signs

In acute ACG the IOP is raised, usually to between 50 and 80 mmHg, and the visual acuity is decreased. The anterior chamber is shallow, usually bilaterally, and the angle is gonioscopically closed in the involved eye. The pupil may be fixed and mid-dilated, and there may be corneal edema and ciliary injection.

Angle grading

Gonioscopy grading is the gold standard for assessing the anterior angle. The Shaffer grading system is used to assess the visibility of the various structures:

Schwalbe’s line (SL), trabeculum (T), scleral spur (SS) and ciliary body (CB):

Grade 4 Wide angle: SL, T, SS and CB visible. Closure not possible
Grade 3 Open angle: SL, T and SS visible. Closure not possible
Grade 2 Moderately narrow angle: SL and T visible. Closure possible, although unlikely
Grade 1 Very narrow angle: only SL and anterior T visible. hligh risk of closure
Grade O Closed angle; no structures visible due to iridocorneal contact.

Van Herick (slit-lamp) estimation involvesfocusing a narrow slit-lamp beam on the cornea immediately adjacent to the temporal limbus, and observing the ratioof the anterior chamber (AC) distance to corneal thickness (CT):

Grade 4 Wide open; AC depth is >50 per cent of CT
Grade 3 Moderately open: AC depth is 25-50 per cent of CT
Grade 2 Narrow: AC depth is 25 per cent ofCT
Grade 1 Very narrow: AC depth is <25 per cent of CT Grade O Closed angle; iridocorneal contact.

The central anterior chamber depth may also be assessed via optical pachometry,
ultrasonography or Smith’s method (slitlamp estimation), with a value of less than 2 mm being considered narrow and at risk of closure.

Prevalence

Acute angle-closure glaucoma is rare in most Western countries, probably owing to the increasing amount of cataract surgery. It remains a significant problem in some developing countries, and is much more common in Chinese and Inuit populations