Glaucoma refers to the optic nerve damage that is caused by a significant rise in intraocular pressure. The raised intraocular pressure is caused by a blockage in aqueous humour trying to escape the eye.
Acute angle-closure glaucoma occurs when the iris bulges forward and seals off the trabecular meshwork from the anterior chamber preventing aqueous humour from being able to drain away. This leads to a continual build-up of pressure in the eye. The pressure builds up particularly in the posterior chamber, which causes pressure behind the iris and worsens the closure of the angle.
Acute angle-closure glaucoma is an ophthalmology emergency. Emergency treatment is required to prevent permanent loss of vision.
The risk factors are slightly different to open-angle glaucoma:
- Increasing age
- Females are affected around 4 times more often than males
- Family history
- Chinese and East Asian ethnic origin. Unlike open-angle glaucoma, it is rare in people of black ethnic origin.
- Shallow anterior chamber
Certain medications can precipitate acute angle-closure glaucoma:
- Adrenergic medications such as noradrenalin
- Anticholinergic medications such as oxybutynin and solifenacin
- Tricyclic antidepressants such as amitriptyline, which have anticholinergic effects
The patient will generally appear unwell in themselves. They have a short history of:
- Severely painful red eye
- Blurred vision
- Halos around lights
- Associated headache, nausea and vomiting
- Hazy cornea
- Decreased visual acuity
- Dilatation of the affected pupil
- Fixed pupil size
- Firm eyeball on palpation
NICE CKS 2019 say patients with potentially life-threatening causes of red eye should be referred for same-day assessment by an ophthalmologist. If there is a delay in admission, whilst waiting for an ambulance:
- Lie patient on their back without a pillow
- Give pilocarpine eye drops (2% for blue, 4% for brown eyes)
- Give acetazolamide 500 mg orally
- Given analgesia and an antiemetic if required
Pilocarpine acts on the muscarinic receptors in the sphincter muscles in the iris and causes constriction of the pupil. Therefore it is a miotic agent. It also causes ciliary muscle contraction. These two effects cause the pathway for the flow of aqueous humour from the ciliary body, around the iris and into the trabecular meshwork to open up.
Acetazolamide is a carbonic anhydrase inhibitor. This reduces the production of aqueous humour.
Secondary Care Management
Various medical options can be tried to reduce the pressure:
- Acetazolamide (oral or IV)
- Hyperosmotic agents such as glycerol or mannitol increase the osmotic gradient between the blood and the fluid in the eye
- Timolol is a beta-blocker that reduces the production of aqueous humour
- Dorzolamide is a carbonic anhydrase inhibitor that reduces the production of aqueous humour
- Brimonidine is a sympathomimetic that reduces the production of aqueous fluid and increase uveoscleral outflow
Laser iridotomy is usually required as a definitive treatment. This involves using a laser to make a hole in the iris to allow the aqueous humour to flow from the posterior chamber into the anterior chamber. The relieves pressure that was pushing the iris against the cornea and allows the humour the drain.
Last updated April 2019