Acute angle-closure glaucoma

• Summary
• Aetiology
• Clinical features
• Diagnosis
• Radiology in Focus
• Optical Coherence Tomography (OCT)
• Ultrasound Biomicroscopy (UBM)
• Management
• References
• Author(s)

Summary

Acute angle-closure glaucoma (AACG) occurs when the anterior chamber angle is obstructed due to the iris bulging forward, preventing the drainage of aqueous humour. This can lead to an increase in intraocular pressure. It presents with severe eye pain, vision loss, headache, nausea and vomiting. Delay in treatment of the acute condition can lead to permanent vision loss, thus AACG is an ophthalmic emergency.

Aetiology

Aqueous humour is produced by the ciliary epithelium in the posterior chamber of the eye. It passes through the pupil into the anterior chamber and drains in the anterior chamber angle, also known as the iridocorneal angle.

There are two main drainage pathways for aqueous humour:

• Canal of Schlemm: most of the aqueous humour drains via the trabecular meshwork into the canal of Schlemm.
• Uveoscleral pathway: a small portion of the aqueous humour drains via the ciliary musle into the suprachoroidal space and supraciliary space.

AACG occurs when the iris bulges forward and blocks the anterior chamber angle. This blocks the drainage of aqueous humour and results in a rapid rise in IOP. The mechanism for this is shown in the diagram below. The pathway for aqueous humour drainage (shown using the blue arrow) is blocked in AACG.

The risk factors for AACG glaucoma include:

• Age
• Ethnicity (people of Asian heritage are more commonly affected)
• Family history
• Gender (females are more commonly affected than males)
• Hyperopia

Clinical features

Symptoms of AACG include:

• Painful, red eye
• Blurred vision
• Halos in the visual field
• Headache
• Nausea and vomiting

Signs of AACG include:

• Conjunctival injection
• Cloudy cornea
• Decreased visual acuity
• Fixed, mid-dilated pupil
• Increased intraocular pressure

Diagnosis

The diagnosis of AACG is made based on the clinical findings and measurement of the intraocular pressure. Normal IOP is 8-21 mmHg. In AACG, the IOP is often very high, such as ≥30 mmHg.

Gonioscopy to examine the anterior chamber angle may be difficult to perform in the affected eye, however, it may be carried out in the unaffected eye to examine for the presence of a narrow anterior chamber angle.

Slit lamp examination and ophthalmoscopy may show optic disc changes consistent with glaucoma such as optic disc cupping.

Radiology in Focus

While clinical examination is essential, various imaging techniques can provide valuable insights into the anatomy of the anterior segment and the extent of angle closure.

Optical Coherence Tomography (OCT)

Anterior segment OCT provides high-resolution cross-sectional images of the anterior chamber and angle structures. It can help assess the anatomy of the angle, measure the angle width, and evaluate any associated changes in the cornea and iris.

AS-OCT can also be used to assess the effects of laser peripheral iridotomy in patients with angle closure:

Ultrasound Biomicroscopy (UBM)

UBM is a high-frequency ultrasound technique that provides detailed images of the anterior segment structures. It is particularly useful in cases where gonioscopy is difficult or inconclusive. UBM can help visualise the angle, iris configuration, and any associated abnormalities.

Management

AACG is an ophthalmic emergency and treatment must be initiated immediately, since delay in treatment can lead to permanent vision loss. The patient requires immediate ophthalmology input and should receive:

• Acetazolamide 500 mg orally: this is a carbonic anhydrase inhibitor which reduces the production of aqueous humour and thereby aims to reduce the IOP.
• Pilocarpine eye drops: this is a miotic agent which causes constriction of the pupil, thereby opening up the pathway for aqueous humour drainage.
• Timolol eye drops: this is a topical beta blocker which reduces the production of aqueous humour and thereby aims to reduce the IOP.
• Analgesia and antiemetic as required.

If intraocular pressure is not responding to initial management, further management options include hyperosmotic agents such as mannitol or glycerol and brimonidine. If medical management fails, anterior chamber paracentesis to remove the aqueous humour directly may be performed.

The definitive management of AACG is laser iridotomy. This involves making a hole in the iris using a laser to allow the passage of aqueous humour from the posterior chamber into the anterior chamber. This breaks the pupillary block and allows the aqueous humour to drain.

References

1. Khazaeni, Babak, and Leila Khazaeni. ‘Acute Closed Angle Glaucoma’. StatPearls, StatPearls Publishing, 2022. PubMed, http://www.ncbi.nlm.nih.gov/books/NBK430857/.
2. ‘Glaucoma: Scenario: acute angle closure and angle closure glaucoma’. NICE, https://www.nice.org.uk/cks-uk-only. Accessed 12 June 2022.

Author(s)

Dr Abhiyan Bhandari

Abhiyan is the Co-Founder and Radiology & Imaging Lead of Ophtnotes. He is a doctor who graduated from UCL Medical School in London. He scored in the top 10% of candidates who sat the Duke Elder examination and runs ophthalmology and Duke Elder revision sessions aimed at medical students. He also runs a YouTube channel aimed at medical students, covering topics ranging from study tips, productivity and vlogs of his journey through medical school.