Angle Closure Glaucoma

In the normal eye, aqueous humour is produced by the ciliary body, behind the iris, and flows through the pupil to drain into the trabecular meshwork which lies around the circumference of the angle between the iris and the cornea. Occasionally, the iris can become apposed to the trabecular meshwork and so block off the aqueous drainage.This situation, known as angle closure glaucoma, results in a rise in intraocular pressure (IOP) which causes a number of symptoms and signs depending on the type of angle closure.

Primary versus secondary angle closure glaucoma

Angle closure can arise as a consequence of the anatomy of the eye: some peoples' angles are naturally very narrow which predisposes the angle to blocking off. Severe hypermetropes fall into this category. In this case it is known as primary acute angle closure. Other susceptible patients include those with a thin iris, a naturally thick lens and a shorter axial length of the eyeball (front to back).¹ Secondary acute angle closure occurs as a result of forces exerted on the iris either anteriorly (e.g. secondary to peripheral anterior synechiae pulling the iris up) or posteriorly (e.g. the lens bulging forward as a result of swelling). Secondary open angle glaucoma refers to the situation where the iridocorneal angle remains open but is blocked off by matter such as blood (from a hyphaema), blood vessels (from poorly controlled advanced diabetic eye disease) or proteins (as seen in hypertensive uveitis). This type of glaucoma is managed within the context of ophthalmology clinics and shall not be further discussed here.

Stages of angle closure glaucoma

In theory, there are five stages in the progression of primary angle closure glaucoma ranging from latent, through to subacute, acute, chronic and absolute - the latter referring to the end-stage of untreated disease which is an irreversibly blind eye. In reality, the subacute and acute closure merge and the acute stage in particular is the one most commonly encountered in a primary care setting. Acute angle closure glaucoma (AACG) is an emergency - prompt diagnosis and treatment is essential to save sight and prophylactic measures will be needed to prevent an attack in the fellow eye. A brief account of chronic angle closure glaucoma is provided at the end of this article.

• This occurs in about 1:1000 people over the age of 40
• It is more common among the South-East Asian population and Eskimos. It is rare among black people.
• It most frequently occurs in the sixth to seventh decade of life
• Females are affected more commonly than males (4:1)
• First degree relatives are at greater risk (eye shape is often inherited)

History

• Pain - this is rapidly progressive and may be confined to the eye but more usually spreads around the orbit with an associated frontal or generalised headache. It is severe. Some individuals - particularly black people (in whom this condition is uncommon) have remarkably little pain but this is not the norm.
• Other ocular symptoms - blurred vision (rapidly progressing to visual loss) and there may be coloured halos around lights. There may be a history of transient blurring of vision and haloes around light suggesting mild, subacute attacks.
• Systemic malaise - nausea and vomiting are common and may be the main presenting feature in some patients¹ - particularly where obtaining a history is a problem (e.g. the demented elderly patient).
• Attack precipitants - a common aetiology of AACG is pupillary block: the mid-dilated pupil snags onto the lens, so causing a build-up of aqueous beneath it which further pushing the iris forward so eventually blocking of the trabecular meshwork. It is therefore not uncommon to hear that the attack came on in situations where there is mid-dilation of the pupil e.g. during a moment of stress or excitement, whilst watching the telly in dim lighting conditions or in patients who are on topical mydriatics or systemic anticholinergics.⁴ The same situation can occasionally occur in older people after long surgery under a general anaesthetic - the lens can accumulate fluid and, in the predisposed individual, bulge forward so also causing a pupillary block.
• Background - a previous history of glaucoma is infrequent and these attacks are usually the first indication of such a problem.

Examination

• The patient is often generally unwell (see symptoms above).
• Examination of the eye shows a red eye (more accurately, a ciliary flush i.e. the redness is more marked around the periphery of the cornea) with a hazy cornea and a non-reactive (or minimally reactive) mid-dilated pupil.
• Palpation of the globe will reveal it to be hard and critically, if you are able to measure the IOP, it will be raised (normal range from ~10-21mmHg, see our dedicated article on examination of the eye).
• Other findings, depending on your expertise with a slit lamp will include shallow anterior chambers in both eyes and corneal epithelial oedema.
• If the acute episode has been precipitated by a secondary cause, there may be evidence of this on examination e.g. peripheral anterior synechiae associated with certain types of uveitis. If the acute rise in IOP has come about on top of a secondary open-angle glaucoma, there may be evidence of trabecular meshwork obstruction due to abnormal deposits clogging it off.
• The acute attack is usually unilateral; however, the predisposing factors are bilateral and long-term management will be to both eyes.

The symptoms and signs - particularly combined - are fairly classic and this acute emergency should be at the forefront of the list of differentials as it is sight threatening and usually reversible. However, if they seem atypical, consider:

• Other causes of acutely raised IOP (usually determined in the eye clinic) e.g. traumatic glaucoma, pigmentary glaucoma, glaucomatocyclitic crisis (Posner-Schlossman syndrome)
• Other causes of acute, severe ocular pain associated with visual loss e.g. corneal disorder, anterior uveitis, scleritis, endophthalmitis, optic neuritis
• Other causes of red eye e.g. conjunctival causes (e.g. keratoconjunctivitis), corneal causes (e.g. keratitis), other causes (e.g. trauma)
• Other causes of general systemic malaise e.g. gastroenteritis

Diagnosis is made on history and examination.

Medical^3,4

• Refer immediately - day or night. These patients need urgent treatment in order to break the attack and save the sight.
• The initial treatment can be summarised as all topical glaucoma medications that are not contraindicated in that patient as well as intravenous acetazolamide.⁵ Some add intravenous osmotics too.
  

  Topical agents (given whilst the acetazolamide is being prepared) include: Β-blockers e.g. timolol 0.5%, one dose - caution in asthmatics and COPD. Steroids e.g. prednisolone 1%, one dose every 15 minutes for an hour then hourly. Apraclonidine 1% (it should be in the fridge), one dose. Patients with their natural lens in: pilocarpine 1-2%, one drop one hour after starting treatment. If they have no natural lens in (e.g. have a history of a cataract extraction in the past): phenylephrine 2.5%, one drop. If not sure about the lens, omit these meds.

• Acetazolamide should be given intravenously (500mg over 10 minutes) and a further 250mg slow release tablet after one hour - check for sulphonamide allergy and sickle cell disease/trait. Patients also need urea and electrolyte monitoring.
• Offer systemic analgesia ± antiemetics.

This should tide the patient over until they are able to be seen by a duty ophthalmologist who will assess the situation hourly initially until the acute attack is broken. These treatments may be repeated depending on the IOP response and a combination of these medications will be given to the patient on discharge. The patient will remain under close observation (e.g. daily clinic reviews if well enough or as an inpatient if there is doubt as to their ability to manage the medication).

Surgical⁶

• Peripheral iridotomy (PI) - this refers to (usually two) holes made in each iris, usually at around the 11 and 2 o'clock positions (they can be seen when assessing the red reflex when they are patent). The idea is to provide a free-flow transit passage for the aqueous to prevent further pupil block. Both eyes are treated as the fellow eye will be predisposed to an acute angle closure attack too. This procedure can usually be carried out within the week following the acute attack, once corneal oedema has cleared enough to provide a good view of the iris.
• Surgical iridectomy - this is carried out where PIs are not possible. It is a less favoured option as it is more invasive and therefore more prone to complications.
• Lensectomy - one of the few situations where cataract surgery is performed on an urgent basis is when the cataractous lens has swollen to precipitate an attack of AACG. The lens is extracted at the earliest opportunity. Beyond this particular cause of AACG, there is some debate as to whether a lensectomy should be routinely performed; it is not the practice in this country.

Other treatment considerations

Breaking the acute attack medically and subsequent PIs should be enough in the management of acute primary angle closure glaucoma. Where the glaucoma is secondary to other factors, these will need addressing in due course.

These include permanent loss of vision, repetition of the acute attack, attack in the fellow eye and central retinal artery or vein occlusion.

In an uncomplicated case of primary acute angle closure glaucoma, the outlook is excellent with full recovery if the diagnosis and treatment are prompt. Delay can lead to complications. Co-morbid pathology will increase the risk of complications (especially if additional treatment is needed) and result in a more guarded prognosis.

The first attack usually comes out of the blue but prophylactic PIs should prevent further problems. It is important that patients are informed about the increased risk to first degree relatives: if they are also found to have shallow anterior chambers, prophylactic PIs can also be carried out to prevent an attack in the first place.

This refers to the situation where there is an insidious, progressive closing off of the trabecular meshwork, so resulting in a gradual rise in IOP. This can arise due to a very gradual thickening of the crystalline lens associated with a predisposing anatomy. It is a bilateral but usually asymmetric condition, affecting women more commonly, particularly hypermetropes.

Patients are usually asymptomatic unless it is very advanced in which case there may be a decreased vision or some degree of peripheral visual field loss, much in the same fashion as in primary open angle glaucoma. Very occasionally, in the advanced stages of the disease, there may be some redness and ocular discomfort but this is not comparable to acute angle closure glaucoma.

Once this condition has been diagnosed, the patient should undergo prompt PIs in both eyes and should be monitored in the eye clinic. Some will need additional medical therapy added to their treatment: the drugs used are the topical glaucoma drugs used for primary open angle glaucoma.