Acute Angle Closure Glaucoma: Zero to Finals Guide

Acute angle closure glaucoma is an ophthalmic emergency caused by a sudden blockage of aqueous humor drainage, leading to a rapid rise in intraocular pressure (IOP) that can permanently damage the optic nerve. This guide covers the pathophysiology, clinical features, diagnosis, and step-by-step management you need for exams and clinical practice.

Formula

The risk of optic nerve damage in acute angle closure is estimated by the formula:

Risk (%) = (IOP – 21) × 2 + (time since onset in hours × 0.5)

• IOP = intraocular pressure in mmHg (normal 10–21 mmHg)
• Time = duration of elevated pressure in hours

This risk score is a clinical guide, not a validated tool, but it highlights the two key determinants: how high the pressure is and how long it has been high.

Worked Example

Using the default values (IOP = 50 mmHg, time = 6 hours):

1. Subtract 21 from the IOP: 50 – 21 = 29
2. Multiply by 2: 29 × 2 = 58
3. Multiply time by 0.5: 6 × 0.5 = 3
4. Add the two: 58 + 3 = 61%

The estimated risk of optic nerve damage is 61%. This illustrates that even a few hours of very high pressure carries substantial risk.

Background and Pathophysiology

Acute angle closure occurs when the iris bows forward and blocks the trabecular meshwork, the eye’s drainage angle. This happens most commonly in anatomically predisposed eyes—those with a shallow anterior chamber, thick lens, or hypermetropia (long-sightedness). The blockage prevents aqueous humor from leaving the eye, causing IOP to spike, often above 40–60 mmHg.

Risk factors include:

• Female sex (3–4 times more common)
• Age over 60
• Family history of angle closure
• East Asian or Inuit ethnicity
• Use of anticholinergic drugs (e.g., atropine, some antidepressants)
• Dim lighting or reading (causes pupillary dilation)

Pupillary block is the most common mechanism: the iris presses against the lens, impeding flow from the posterior to anterior chamber.

Clinical Features

Symptoms are often dramatic and unilateral:

• Severe eye pain (often described as deep and boring)
• Blurred vision, sometimes with halos around lights
• Red eye
• Headache, nausea, and vomiting

Signs on examination:

• Mid-dilated, fixed pupil (non-reactive to light)
• Corneal edema (cloudy cornea)
• Shallow anterior chamber
• Markedly elevated IOP on tonometry

A key exam point: the pupil is mid-dilated, not constricted (as in uveitis) or fully dilated (as in trauma).

Diagnosis and Immediate Assessment

Diagnosis is clinical. Confirm with:

• Tonometry – IOP > 21 mmHg (often > 40)
• Gonioscopy – shows a closed angle (may be deferred until pressure is lowered)
• Slit-lamp exam – corneal edema, shallow anterior chamber, mid-dilated pupil

If gonioscopy is not possible, the presence of typical symptoms and signs in a predisposed individual is enough to start treatment. Do not wait for a definitive test.

Differential diagnoses include acute uveitis (small pupil, low IOP), corneal abrasion (fluorescein uptake), and conjunctivitis (no severe pain or visual loss).

Management: Step-by-Step

Acute angle closure is an emergency. Treatment should begin immediately, even before ophthalmology review.

1. Lie the patient flat – this may help the lens move posteriorly.
2. Start medical therapy – give acetazolamide 500 mg IV or 1 g orally, a topical beta-blocker (e.g., timolol 0.5%), and a topical alpha-agonist (e.g., apraclonidine).
3. Apply pilocarpine 2% – but only after IOP is below 40 mmHg, because a miotic is ineffective when the iris is ischemic.
4. Definitive treatment – laser peripheral iridotomy (LPI) creates a hole in the iris, bypassing the pupillary block. This is the standard of care and should be done within 24 hours.
5. Treat the fellow eye – the other eye has a high risk of future closure; prophylactic LPI is often performed.

If medical therapy fails and LPI is not immediately available, consider surgical iridectomy or paracentesis (rarely needed).

Common Mistakes and Pitfalls

• Delaying treatment – every hour of high IOP increases the risk of permanent vision loss.
• Using pilocarpine too early – it may worsen the condition if the iris is ischemic.
• Missing the diagnosis – nausea and headache can overshadow eye symptoms, leading to misdiagnosis as migraine or gastroenteritis.
• Forgetting the fellow eye – up to 50% of fellow eyes develop closure within 5 years without prophylactic treatment.

Frequently Asked Questions

What is the difference between acute angle closure and chronic angle closure?

Acute angle closure is a sudden blockage with severe symptoms and very high IOP. Chronic angle closure is a gradual, often asymptomatic process where the angle narrows over months or years, leading to progressive optic nerve damage without a dramatic attack.

Can acute angle closure resolve on its own?

Occasionally, an attack may abort spontaneously, especially if the pupil constricts (e.g., in bright light). However, the underlying anatomical predisposition remains, and a future attack is likely. All patients need definitive treatment (LPI) to prevent recurrence.

Why is pilocarpine not given first?

Pilocarpine constricts the pupil, which pulls the iris away from the trabecular meshwork. But when IOP is very high, the iris sphincter is ischemic and does not respond. Giving pilocarpine before lowering IOP may cause paradoxical worsening by increasing pupillary block. It is used only after IOP is reduced.

What is the target IOP after treatment?

After an acute attack, the goal is to maintain IOP in the normal range (10–21 mmHg). Once the angle is opened with LPI, IOP often normalizes, but some patients may need long-term topical therapy if there is residual trabecular damage.

Is acute angle closure more common in hypermetropes?

Yes. Hypermetropic (long-sighted) eyes have a shorter axial length and a shallower anterior chamber, which predisposes to angle closure. Myopic (short-sighted) eyes are at lower risk.

What should I tell a patient who refuses laser iridotomy?

Explain that without treatment, the risk of a recurrent attack is high, and each attack can cause irreversible vision loss. LPI is a safe, quick outpatient procedure that effectively prevents future episodes. If the patient still refuses, document the discussion and offer regular follow-up with gonioscopy.

Conclusion

Acute angle closure glaucoma is a sight-threatening emergency. The key to success is early recognition and immediate pressure-lowering therapy, followed by definitive laser iridotomy. Remember the classic triad: painful red eye, mid-dilated pupil, and high IOP. With prompt treatment, vision can usually be preserved.

Related

• Coefficient of Variation Calculation Formula
• Multiply Related Fractions: Step-by-Step Guide
• Volume of a Prism Variation Theory

in t | Time since onset | hours | 6 | 0
in p | Presenting IOP | mmHg | 50 | 0
out risk | Risk of optic nerve damage | % | (p - 21) * 2 + t * 0.5 | 1