What is it?
A sudden increase in intraocular pressure, which can present as an ophthalmic emergency.
It usually occurs when the angle between the cornea and iris suddenly becomes closed.
The diagram below shows the normal anatomy of the human eye, focusing in on the problem area. The trabecular meshwork is a drainage pathway for aqueous humor within the eye. Aqueous humor is unusual in that it flows back to front.
When there is a disruption to flow – in this case, due to an acute closure of the drainage pathway the pressure builds until it becomes dangerously high and threatens the patient’s vision as it can lead to irreversible optic nerve damage. A common cause of anterior chamber angle closure is pupillary block, which occurs when aqueous humour outflow is obstructed due to contact between the iris and lens.
Who gets it?
- It affects approximately 2 per 100,000 per year (1)
- Typically more common in females
The royal college states certain risk factors for AACG such as:
- Hypermetropia (being long sighted, especially more than +6)
- Concomitant use of other anticholinergic agents eg antidepressants
- Diabetes: (as typically diabetics have higher exposure to dilating eye drops which can increase the risk of acute angle closure).
- Living in an area not close to emergency eye centers as this could delay vital treatment
- Family history of AACG
How do I diagnose it?
Clinical symptoms include:
- Fixed, mid-dilated pupil
- Unilateral painful red eye
- Blurred vision
- Halos around lights (most common)
- Hard/firmer eyeball on palpation (compare with the other eye)
- Corneal oedema may be present
- Associated systemic symptoms such as nausea, vomiting and feeling unwell – particularly if pressures are very high.
If a patient presents with any of the above – an urgent referral to Ophthalmology and advise them to go to their nearest eye casualty to be assessed.
In an Ophthalmic setting – AACG is typically diagnosed when looking at the patient under the slit-lamp to observe the above symptoms and using the goldmann’s tonometer to measure the pressure. Normal pressure is around 21mmHg; typically in AACG it can be anything from >30 to >40 or even higher! Gonioscopy should also be performed but may be difficult to visualise the angle if the cornea is oedematous.
Okay we think they have it, how do I treat it?
- NICE guidance advises if a diagnosis of AACG is suspected – admit and await urgent Ophthalmology assessment
- Medical management of pressure lowering drops which have different mechanisms on the aqueous flow including Beta blockers such as timolol, Acetazolamide can be given orally or IV.
- Topical pilocarpine: a miotic that constricts the pupil and increases aqueous humour outflow.
- In some settings with dangerously high pressures and systemic symptoms, the clinician may start mannitol and admit the patient for close monitoring.
- Advise patients to avoid dim light, as this can exacerbate the narrow angle and make the attack worse!
- Ophthalmologists may also consider laser/ surgical options such as PI (peripheral iridotomy), lens extraction or trabeculoplasties where specialist pressure lowering devices are implanted into the eye.
- If admission is not possible in the setting eg primary care – NICE advises: lying the person flat with their face up – as this may relieve some of the pressure on the angle, and then medically managing the patient with pilocarpine eye drops (2% in blue eyes and 4% in brown eyes) and giving oral acetazolamide 500mg PO.
- Irreversible optic nerve damage leading to permanent sight loss
- Development of synechiae (abnormal adhesions within the eye)
- Chronic angle closure problems
- The Management Of Angle-Closure Glaucoma – Royal college of ophthalmologists
Written by Dr Shuchi Kohli (FY2) & reviewed by Dr Kate Reed (Ophthalmology ST4).
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