13th December 2023

Anterior chamber

Acute angle-closure glaucoma (AACG) is an ophthalmic emergency. The normal range for intraocular pressure is 10 to 22 mmHg. Aqueous humor production begins in the ciliary body, flows through the pupil, and exits the eye through the trabecular meshwork and Schlemm’s canal in the anterior chamber angle (between the iris and the cornea). In acute angle-closure glaucoma, the intraocular pressure increases rapidly due to obstruction of the drainage angle and blockage of aqueous humor outflow. Predisposing factors include an anatomically narrow anterior chamber angle, increasing lens size and an anteriorly located iris-lens diaphragm. AACG is often precipitated by pupillary dilatation. As the pupil enlarges, the peripheral iris contacts the lens, preventing the flow of aqueous through the pupil (pupillary block). This leads to bulging of the iris (iris bombe), crowding of the anterior chamber angle by the iris and obstruction of aqueous humor outflow. The intraocular pressure rises acutely, leading to symptomology.

Risk Factors

• Age: The average age at presentation is 60. This is felt to be due to the increasing size of the lens with age
• Gender: F:M ratio 4 to 1
• Ethnicity: more common in Southeast Asians, Chinese, and Inuit heritage
• Family history: An anatomically narrow anterior chamber angle is usually inherited

Clinical Presentation

• Reduced vision associated with haloes
• Severe headache
• Nausea & vomiting
• Abdominal pain
• Red, injected eye
• Cloudy cornea
• Fixed, semi-dilated pupil (iris ischaemia)
• Intraocular pressures commonly >50mmHg (normal 11-2mmHg)
• Glaucomatous or swollen optic disc

Management

The medical treatment for AACG aims to:

1. Decrease production of aqueous humor
2. Restore aqueous outflow
3. Relieve pupillary block

Initial medical therapy includes a combination of the following medications:

• Intravenous acetazolamide 500 mg, topical beta-blocker (timolol 0.5%) and alpha 2-agonist (apraclonidine 1%) to block the production of aqueous humor.
• Topical pilocarpine 1% to 2% to constrict the pupil and increase the outflow of aqueous humor.
• If the intraocular pressure remains elevated after an hour, intravenous mannitol 1 gram/kg can be given (if there is no contraindication) to rapidly reduce the volume of aqueous humor.

Definitive treatment is by laser peripheral iridectomy (PI) after the acute episode subsides. Iridectomy relieves the pupillary block by allowing the flow of aqueous humor through the iris. The contralateral eye usually has the same predisposing anatomy and carries up to 80% risk of developing an attack of AACG if untreated. Hence, PI is usually performed in both eyes following a first presentation.

Prognosis

The outcome for patients with AACG is good following treatment if recognised early. In the early stages, corneal clouding may be subtle and overlooked. Patients may be mistakenly worked up for intracranial or abdominal symptoms. Delay in treatment can lead to damage to the optic nerve and vision loss.

Image Source: Wikimedia Commons (2011). Acute Angle Closure-glaucoma, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Acute_Angle_Closure-glaucoma.jpg (Accessed on: 15  May 2022).