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OP7.3 | Primary Angle Closure Glaucoma — SDL Guide (Part 2)

Diagnosis: PACS, PAC, and PACG Spectrum

Primary angle-closure disease exists on a spectrum, and recognising where a patient sits on this spectrum determines both the urgency and the nature of treatment. The spectrum was formally classified by the International Society of Geographical and Epidemiological Ophthalmology (ISGEO) as follows:

Primary Angle-Closure Suspect (PACS): The iridocorneal angle is occludable on gonioscopy (pigmented trabecular meshwork not visible in ≥180 degrees of angle in the primary position) but without peripheral anterior synechiae, raised IOP, or optic nerve damage. The eye is at risk but has not yet closed. Treatment: monitoring ± prophylactic laser peripheral iridotomy (LPI) — the evidence from the ZAP trial (2016) was that routine LPI in all PACS did not significantly reduce conversion to PAC over 6 years, moderating the enthusiasm for universal prophylaxis, but it remains widely practised in South Asia.

Primary Angle Closure (PAC): Occludable angle with either raised IOP (>21 mmHg) or peripheral anterior synechiae (PAS — permanent adhesions between peripheral iris and trabecular meshwork), but WITHOUT glaucomatous optic neuropathy. Treatment: LPI to relieve pupil block; IOP-lowering drops if needed.

Primary Angle Closure Glaucoma (PACG): PAC WITH glaucomatous optic nerve damage (increased C:D ratio, RNFL loss) and corresponding visual field defects. Treatment: LPI + IOP-lowering drops + possible surgery.

Acute PACG Attack (Acute Angle-Closure Crisis): Sudden, complete angle closure with dramatically elevated IOP (50–80+ mmHg) — an ophthalmic emergency requiring immediate intervention.

Differential diagnosis of acute red painful eye — the SIGHT-THREATENING causes must always be excluded:

Condition	Pain	Vision	Cornea	Pupil	IOP	Discharge	Key feature
Acute PACG	Severe	Reduced, haloes	Hazy, oedematous	Mid-dilated, fixed	50–80+ mmHg	None	Rock-hard eye; nausea/vomiting
Microbial keratitis	Moderate-severe	Reduced	Ulcer with infiltrate	Normal	Normal or slightly ↑	Mucopurulent	Hypopyon; history of contact lens/injury
Anterior uveitis	Moderate	Slightly reduced	KPs (keratic precipitates)	Small, irregular (posterior synechiae)	Low or mildly ↑	None	Ciliary flush; photophobia; systemic disease
Scleritis	Severe, boring	Usually normal	Normal	Normal	Normal	None	Violaceous scleral swelling; deep pain
Bacterial conjunctivitis	Mild/gritty	Normal	Clear	Normal	Normal	Mucopurulent	NO vision loss; no ciliary flush

The three reliable danger signs that distinguish SIGHT-THREATENING from SAFE acute red eye: (1) reduced vision, (2) photophobia/pain, (3) ciliary flush. Any of these → urgent ophthalmology. Simple conjunctivitis has none of these danger signs.

Emergency and Definitive Management

The management of an acute PACG attack requires rapid, simultaneous, multi-drug attack on the elevated IOP, followed by definitive intervention to eliminate the pupil block mechanism permanently. Treatment delay directly translates to optic nerve damage and a greater risk of permanent field loss.

IMMEDIATE (Emergency) PHASE — lower IOP urgently:

Step 1 — Osmotic agent (most potent IOP reducer):
Intravenous mannitol (20% solution, 1–2 g/kg body weight, infused over 30–60 minutes) is the fastest and most powerful means of lowering IOP in an acute attack. It acts as an osmotic diuretic, creating a osmotic gradient that draws fluid from the vitreous body into the bloodstream, shrinking vitreous volume and rapidly reducing IOP. Contraindications: congestive cardiac failure, renal failure (inability to excrete osmotic load). If IV mannitol is unavailable, oral glycerol (glycerin 50%, 1 mL/kg) can be used — less effective and causes nausea, limiting use in already nauseated patients.

Step 2 — Systemic carbonic anhydrase inhibitor (CAI):
Intravenous acetazolamide (500 mg IV, followed by 250 mg QID oral) reduces aqueous production by inhibiting carbonic anhydrase in the ciliary epithelium. It begins working within 30–60 minutes and provides sustained IOP reduction. In areas without IV access, oral acetazolamide 500 mg can be used initially.

Step 3 — Topical miotic: Pilocarpine 2% (THE KEY DRUG for angle opening):
Pilocarpine (a muscarinic agonist) constricts the pupil by contracting the iris sphincter, which pulls the peripheral iris away from the trabecular meshwork, mechanically opening the iridocorneal angle. Applied as 2% drops every 15 minutes × 2 doses to the affected eye initially. CRITICAL: At very high IOP (>60–70 mmHg), the iris sphincter is ischaemic and cannot respond to pilocarpine — the drug should still be applied as IOP begins to fall with other agents, at which point the sphincter recovers and pilocarpine becomes effective. ALSO APPLY TO THE FELLOW EYE as prophylactic 1% pilocarpine to prevent an attack in the contralateral predisposed eye.

REMINDER — NEVER confuse this with POAG treatment: pilocarpine is RIGHT for angle closure (mechanically opens the angle) but is NOT appropriate for POAG (open-angle — the angle is already open; pilocarpine adds myopia and side effects without mechanism-specific benefit).

Step 4 — Topical beta-blocker:
Timolol 0.5% (or betaxolol 0.25% if asthma present) reduces aqueous production, adding to IOP reduction. Apply twice.

Step 5 — Supine positioning:
Have the patient lie flat on their back with face upward. Gravity pulls the lens and vitreous posteriorly, slightly deepening the anterior chamber and relieving some of the pupil block — a simple, zero-cost adjunct.

DEFINITIVE TREATMENT — Eliminate pupil block:

Laser Peripheral Iridotomy (LPI):
Once IOP has been reduced to ≤35 mmHg and the cornea has cleared sufficiently to allow laser aiming, Nd:YAG laser peripheral iridotomy is performed. This creates a small full-thickness hole in the peripheral iris, providing an alternative route for aqueous to flow directly from the posterior chamber to the anterior chamber, bypassing the pupil aperture entirely. With pupil block eliminated, the iris flattens back, the angle opens, and the IOP normalises. LPI is performed on BOTH eyes — the treated eye for cure and the fellow eye prophylactically.

Surgical iridectomy: If LPI fails or the cornea remains too cloudy for laser, a surgical peripheral iridectomy is performed under general anaesthesia.

Clear Lens Extraction (CLE):
The EAGLE trial (2016) demonstrated that early clear lens extraction (phacoemulsification with IOL) for PAC and PACG (not just acute attacks) achieved superior IOP control and better quality of life compared to LPI alone, challenging the traditional LPI-first approach. CLE removes the thick crystalline lens (a major contributor to angle crowding) entirely, permanently deepening the anterior chamber. It is increasingly offered to patients who are symptomatic or have PAC/PACG with cataract.

Summary of management sequence:
1. IV mannitol → 2. IV/oral acetazolamide → 3. Pilocarpine 2% drops → 4. Topical timolol → 5. Supine position → 6. Nd:YAG LPI (after IOP reduction, cornea clear) → 7. Prophylactic LPI to fellow eye → 8. Long-term IOP monitoring + field/disc review

Self-Assessment: Clinical Reasoning in PACG

Having worked through the full arc of primary angle-closure glaucoma — from the acute attack through its underlying anatomy, examination, diagnostic spectrum, and emergency and definitive management — you are now ready to integrate this knowledge through clinical reasoning scenarios that reflect the decisions you will face as a junior doctor or in an OSCE.

Scenario 1: A 52-year-old hypermetropic woman comes to your OPD for refraction. During the examination you notice the anterior chamber appears very shallow on slit-lamp. Her IOP is 19 mmHg. Her optic discs look healthy. She has no symptoms. What do you do? This is a primary angle-closure suspect (PACS). She has not had an attack — her IOP and discs are currently normal — but her shallow anterior chamber places her at anatomical risk. The correct action is gonioscopy to document the angle grade, measurement of anterior chamber depth, and referral to a glaucoma specialist to discuss prophylactic laser peripheral iridotomy. She should be counselled about precipitants: avoid prolonged time in very dark environments, tell every prescribing doctor that she has a narrow angle (many drugs — antihistamines, antispasmodics, tricyclic antidepressants, even inhaled bronchodilators — can precipitate an attack in a predisposed eye).

Scenario 2: You are the medical officer on call at a district hospital. A 60-year-old man arrives at 10 PM with a painful red right eye, nausea, and IOP of 64 mmHg on your Perkins tonometer. No ophthalmologist is available until morning. What can you safely initiate? IV mannitol 20% at 1–2 g/kg over 30–60 minutes (check no cardiac failure or renal failure); IV acetazolamide 500 mg; pilocarpine 2% drops every 15 minutes for 2 doses; topical timolol 0.5%; supine positioning. These measures will begin IOP reduction while you organise urgent ophthalmology review. Document your actions and the time. Do not wait passively — the optic nerve is under ischaemic stress at 64 mmHg.

Scenario 3: After successful emergency management, a patient's IOP falls to 22 mmHg and the cornea clears. The ophthalmologist performs Nd:YAG LPI to the right eye and recommends prophylactic LPI to the left eye the same day. The patient declines the left eye treatment: 'That eye is fine, why would I do it?' How do you counsel her? The left eye has the same narrow-angle anatomy and carries a cumulative lifetime risk of an acute attack estimated at 40–80% without prophylaxis. An untreated fellow eye is not 'fine' — it is a time bomb with a predisposing anatomy identical to the one that caused tonight's emergency. The LPI procedure takes minutes, has a very low complication rate, and eliminates the pupil-block mechanism permanently.