Glaucoma refers to a collection of disorders resulting in progressive optic neuropathy in which raised intraocular pressure is typically a key factor.
Glaucoma is a common pathology affecting the eye that untreated can result in significant loss of vision. Worldwide it is the leading cause of irreversible blindness with 66 million affected, 12.5 million of whom are blind. In the UK it is responsible for around 10% of those registered blind. There are two major forms of glaucoma (and a related condition ocular hypertension):
In this note we focus on angle-closure glaucoma. Though less common than open-angle glaucoma, it causes around 50% of cases of glaucoma-related blindness. It may be classified as acute or chronic with differing presentations:
As described above angle-closure glaucoma can also be divided into primary angle-closure glaucoma (PACG) and secondary angle-closure glaucoma (when it occurs secondary to another eye condition). PACG is by far the more common form.
Primary-angle closure glaucoma affects around 0.4% of those over the age of 40 in the UK.
It becomes increasingly common with advancing age. The condition is around 2-4 times more common in women.
Those of Asian and Inuit heritage are more commonly affected with prevalence highest in China.
Women are 2-4 times more likely to be affected than men.
There are a number of risk factors for angle-closure. Interestingly a number differ to open-angle glaucoma with hyperopia (as opposed to myopia) and those of Asian and Inuit heritage (as opposed to Black African) more likely to be affected.
Aqueous humour is produced by epithelium covering the ciliary bodies in the posterior chamber of the eye.
The eye may be divided into three chambers:
The aqueous humour is produced and actively secreted by the ciliary epithelium located in the posterior chamber of the eye. It is a watery fluid with a similar make-up to plasma though with a far lower protein content.
NOTE: Inflammation of the uvea can lead to increased membrane permeability and therefore protein content in the aqueous humour. This can scatter light resulting in flare.
The aqueous humour passes through the pupil into the anterior chamber and drains at the anterior chamber angle (iridocorneal angle). There are two drainage pathways:
Angle closure glaucoma may be primary (anatomical predisposition) or secondary (occurring due to another eye pathology).
In PACG patients are anatomically predisposed to the conditions development. The lens is located anteriorly and presses against the iris.
This interrupts normal flow through the chambers with pressure building in the posterior chamber behind the iris. As the iris pushes forward it closes the anterior chamber angle.
Furthermore contact with the iris leads to scar tissue formation within the trabecular meshwork further reducing drainage.
PACG may be acute, subacute or chronic:
Secondary angle-closure glaucoma results from other pathology in the eye that result in angle closure - they are far less common than PACG.
The causative pathologies can be divided into conditions that ‘push’ the iris/ciliary body (e.g. space occupying lesion) or those that ‘pull’ the iris causing deformity (e.g. neovascularisation of iris).
Angle-closure glaucoma may present with acute severe eye symptoms or have a chronic and insidious onset.
The symptoms experienced by the patient depend on the degree of angle closure and the extent and speed with which IOP rise.
Patients with acute angle-closure glaucoma present with acute and severe symptoms. They may have a history of previous similar episodes that resolved.
Hstory may reveal a precipitating factor such as a topical pupil dilator or watching television in a darkened room. Features include:
Patients with chronic disease are normally asymptomatic. Similarly to POAG it may be picked up on routine ophthalmic examination.
Others may present with advanced disease when visual loss becomes noticeable to the patient.
Acute angle-closure glaucoma should be suspected in patients presenting with a painful red eye and visual disturbance.
Investigations are dependent on the presentation. Acute angle-closure glaucoma is normally suspected based upon the clinical presentation. Diagnosis may be made with:
Further investigations may include ultrasound biomicroscopy and optical coherence tomography.
Acute angle-closure glaucoma is an ophthalmic emergency requiring immediate ophthalmology input and management.
The aim of initial therapy is to reduce the IOP, improve symptoms and preserve sight. In addition to medication that reduce IOP, antiemetics and analgesics may be required.
A number of medical therapies may be used:
If medical management fails, anterior chamber paracentesis may be performed to ensure resolution.
After the initial presentation has been managed a definitive treatment, aimed at creating a persistent open-angle is required.
Laser peripheral iridotomy involves creating an opening in the iris. This allow equalisation between the posterior and anterior chambers thereby preventing a build up of pressure in the posterior chamber. Typically treatment will also be advised in the contralateral eye which is also at risk of angle-closure.
Chronic angle-closure glaucoma may also be treated with laser peripheral iridotomy.
Laser peripheral iridotomy can be used in patients with chronic angle-closure glaucoma. Again it resolves ‘pupillary block’ as it allows equalisation between the posterior and anterior chambers thereby preventing a build up of pressure in the posterior chamber.
Treatment failure may occur, especially if there is significant scarring of the trabecular meshwork from previous apposition with the iris. Treatment is then similar to that of open-angle glaucoma.
Angle-closure glaucoma is responsible for 50% of the glaucoma-related blindness in the world.
This translates to around 6.25 million people, despite being less common than the open-angle form. If recognised and promptly treated the prognosis is good but the insidious nature of the chronic form and lack of access to advanced healthcare often leads to poor outcomes.
40-80% of patients with an acute angle-closure glaucoma will have an episode in the contralateral eye in the following 5-10 years. As such after an acute episode in one eye, definitive treatment is advised in the other.
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