Primary Angle Closure Glaucoma

Two segments and two chambers

The eye consists of an anterior and posterior segment, and the posterior aspect of the lens and ciliary body acts as the boundary between the two. The anterior segment of the eye can be further subdivided into anterior and posterior chambers. The iris marks the distinction between anterior and posterior chambers, the pupil acting as a conduit between these two communicating fluid-filled compartments. This fluid is the aqueous humour (not to be confused with the vitreous humour contained within the posterior segment).

The flow of Aqueous humour

The aqueous humour is produced by the ciliary body and helps maintain fluid pressure and also provides nutrition to the tissues (4). The aqueous flows from the ciliary body anteriorly, through the pupil and then to the angle created by the iris and cornea, where it drains by two main pathways. The conventional or trabecular outflow pathway is the means by which most of the fluid will drain. First the aqueous enters the trabecular meshwork, then into Schlemm’s canal and finally into the episcleral veins via the collector channels (5). This drainage is crucial to maintain stable intraocular pressures and a healthy functioning eye and optic nerve.

There are many mechanisms by which outflow of the aqueous humour from the anterior chamber can be obstructed resulting in pathology. The mechanism discussed in this module is acute angle closure.

The chain of events in PACG starts with closure of the angle, between the cornea and iris, which impedes the flow of aqueous humour, resulting in increased intra-orbital pressures (IOP). If the pressure remains high enough, optic neuropathy (pathology of the optic nerve) and loss of vision can ensue (2).

What can cause closure of the angle?

Closure of the angle occurs when the iris comes forward, towards the trabecular meshwork. The most common way in which this is occurs, is when the pupillary portion of the iris is in close proximity to the lens, making it more difficult for aqueous humour to flow into the anterior chamber. This increase in resistance, results in a bowing of the iris anteriorly and narrowing (closure) of this angle. This mechanism is called pupillary block (2).

Risk factors for angle closure glaucoma (6)(7)(8):

• Female gender
• increasing age
• Inuit or Asian ethnicity
• previous PACG in contralateral eye
• Hyperopia
• Anatomic risk factors: Short axial length, Anterior chamber depth of <2.5mm, Increased lens volume, Increased choroidal thickness, angle anatomy

PACG tends to occur in people with small eyes (these patients tend to be hyperopic; long-sighted – usually needing glasses for reading from a young age ).

PACG presentation can be acute or chronic depending on the speed of angle closure. Acute angle closure is a medical emergency and should be in the differential diagnosis of acute headache but would be associated with red eye and blurred vision. Acute attacks are often precipitated by pupil dilation (This is because when the pupil is mid-dilated the pupillary portion of the iris is at its closes to the lens, increasing the likelihood of the pupillary block occurring), which can be a physiological reflex to low light conditions or induced by certain medications with a mydriatic effect (pupil dilating).

Symptoms (7)(2)(9):

• rapid loss of vision in one or both eyes
• pain of and around the eye. Which can often be intense.
• nausea and vomiting
• blurred vision
• coloured haloes seen around lights

Signs (8):

• reduced visual acuity
• red eye
• corneal oedema
• fixed mid-dilated pupil

If the closure of the angle can be stopped, PACG can be prevented to a degree (2).

Treatment of PACG (10)

If admission to a secondary care facility, where assessment by an Ophthalmologist cannot immediately take place:

• lying the patient supine can take pressure off the angle, and pilocarpine drops,  a miotic (pupil constricting) medication can be administered to help aid aqueous outflow.
• acetazolamide (carbonic anhydrase inhibitor) can be given orally which helps to reduce aqueous humour production, reducing intraocular pressure
• antiemetics and analgesia can be given as required

Once in a secondary care environment eye drop combinations can consist of:

• carbonic anhydrase inhibitor +/- beta-blocker (eg timolol) +/- alpha-2 agonist (eg apraclonidine). These medications work by suppressing aqueous humour formation (8).
• Interestingly, pilocarpine (muscarinic agonist) is reserved for certain cases, as in addition to its miotic effect, it can actually cause the ciliary body to contract, further reducing the anterior chamber depth and subsequently further exacerbate angle closure (2)
• Mannitol (a hyperosmotic agent) can also be administered when intraocular pressures are especially high, or when cases are refractory to initial treatment (8)

As discussed above, pupillary block is the mechanism which is most often implicated in PACG. Thus, creating a small hole in the iris with a laser (laser peripheral iridotomy or LPI) will allow aqueous humour to flow. LPI is the definitive management following initial treatment (2)(8).

It is worth noting that as we age the lens in our eyes enlarges, which in people with small eyes can lead to pupil block. Cataract surgery is a very effective way of opening the drainage angle and treating acute angle closure. Acute angle closure is very unlikely in patients who have had previous cataract surgery.

1. Weinreb RN, Aung T, Medeiros FA. The Pathophysiology and Treatment of Glaucoma: A Review. JAMA [Internet]. 2014 May 14 [cited 2022 May 11];311(18):1901. Available from: /pmc/articles/PMC4523637/
2. Sun X, Dai Y, Chen Y, Yu DY, Cringle SJ, Chen J, et al. Primary angle closure glaucoma: What we know and what we don’t know. Prog Retin Eye Res. 2017 Mar 1;57:26–45.
3. Glaucoma – American Family Physician [Internet]. [cited 2022 May 11]. Available from: https://www.aafp.org/afp/2016/0415/p668.html
4. Aqueous Humor Flow and Function | BrightFocus Foundation [Internet]. [cited 2022 May 11]. Available from: https://www.brightfocus.org/glaucoma/infographic/aqueous-humor-flow-and-function
5. Goel M, Picciani RG, Lee RK, Bhattacharya SK. Aqueous Humor Dynamics: A Review. Open Ophthalmol J [Internet]. 2010 Sep 22 [cited 2022 May 11];4(1):52. Available from: /pmc/articles/PMC3032230/
6. Khazaeni B, Khazaeni L. Acute Closed Angle Glaucoma. StatPearls [Internet]. 2022 Jan 5 [cited 2022 May 11]; Available from: https://www.ncbi.nlm.nih.gov/books/NBK430857/
7. Anwar F, Turalba A. An Overview of Treatment Methods for Primary Angle Closure. https://doi.org/101080/0882053820161228386 [Internet]. 2016 Jan 2 [cited 2022 May 11];32(1):82–5. Available from: https://www.tandfonline.com/doi/abs/10.1080/08820538.2016.1228386
8. Angle-closure glaucoma – Treatment algorithm | BMJ Best Practice [Internet]. [cited 2022 May 12]. Available from: https://bestpractice.bmj.com/topics/en-gb/372/treatment-algorithm#patientGroup-0-0
9. Primary Angle Closure / Primary Angle Closure Glaucoma (PAC / PACG) – College of Optometrists [Internet]. [cited 2022 May 12]. Available from: https://www.college-optometrists.org/clinical-guidance/clinical-management-guidelines/primaryangleclosure_primaryangleclosureglaucoma_pa
10. Scenario: Acute angle closure and angle closure glaucoma | Management | Glaucoma | CKS | NICE [Internet]. [cited 2022 May 12]. Available from: https://cks.nice.org.uk/topics/glaucoma/management/acute-angle-closure-angle-closure-glaucoma/