Primary Angle-Closure Glaucoma

Primary angle-closure glaucoma (PACG) is a sight-threatening optic neuropathy caused by apposition or synechial closure of the iridocorneal angle, obstructing aqueous outflow and raising intraocular pressure (IOP). Acute PACG (acute congestive glaucoma) is one of the few true ophthalmic emergencies and a perennial NEET PG favourite — the classic red eye with haloes, a fixed mid-dilated pupil, a stony-hard globe, and IOP often above 50 mmHg.

Definitions and the spectrum of angle closure

Angle closure is defined by iridotrabecular contact (ITC) — apposition of peripheral iris to the trabecular meshwork. The disease evolves along a recognised spectrum, and naming the correct stage is frequently tested.

Stage	Term	Angle	IOP	Optic disc / field	Symptoms
1	Primary angle-closure suspect (PACS)	Occludable (ITC ≥180° on gonioscopy)	Normal	Normal	None
2	Primary angle closure (PAC)	ITC + raised IOP and/or peripheral anterior synechiae (PAS)	Raised	Normal	Usually none
3	Primary angle-closure glaucoma (PACG)	ITC + PAS/raised IOP	Raised	Glaucomatous damage present	Variable

High-yield: Glaucomatous optic neuropathy (disc cupping/field loss) must be present to call it PACG. Without disc/field damage it is PAC or PACS — angle closure alone is not glaucoma.

Clinically, angle closure presents in three patterns: acute (sudden congestive attack), subacute/intermittent (recurrent self-limiting episodes, typically in dim light), and chronic (creeping synechial closure, often asymptomatic, mimicking POAG).

Predisposing anatomy and risk factors

PACG occurs in eyes that are anatomically predisposed to a crowded anterior segment. Recognising the at-risk eye is heavily examined.

• Hypermetropia (hyperopia) — short axial length, shallow anterior chamber.
• Shallow anterior chamber (axial depth <2.5 mm).
• Large/anteriorly positioned lens — thick lens, age-related lens growth, anterior lens position.
• Small corneal diameter and steep cornea.
• Female sex (3–4× more common; shallower chambers).
• Age > 40–50 years (lens thickening).
• Asian / Inuit ethnicity — PACG is the leading cause of glaucoma blindness worldwide because of high prevalence in East Asia.
• Positive family history and short stature.

High-yield: Hypermetropic, middle-aged Asian woman with a shallow anterior chamber = the classic PACG candidate. POAG, in contrast, is associated with myopia.

Mnemonic for predisposing eye — "SHALLOW": Short axial length, Hypermetropia, Anterior lens, Large lens, Low chamber depth, Older age, Woman.

Pathophysiology — the central concept of pupillary block

The dominant mechanism in primary angle closure is relative pupillary block.

Mechanism (flow): Aqueous secreted by ciliary body → must pass between posterior iris surface and anterior lens to reach the anterior chamber → in a crowded eye the iris–lens contact resists flow → aqueous accumulates behind the iris → raised posterior chamber pressure → peripheral iris bows forward (iris bombé) → peripheral iris contacts trabecular meshwork → angle closes → outflow obstructed → IOP rises.

The block is maximal at a mid-dilated pupil (3.5–6 mm), where iris–lens apposition is greatest AND the peripheral iris is most flaccid/bunched. This is why attacks are precipitated by:

• Dim illumination (cinema, evening) → physiological mid-dilation.
• Emotional stress / sympathetic surge → mydriasis.
• Mydriatic drops (atropine, tropicamide) and dilatation for fundus exam.
• Systemic anticholinergics / sympathomimetics — antihistamines, tricyclics, nebulised ipratropium, decongestants.
• Prone position / dark reading.

High-yield: Pilocarpine (a miotic) relieves pupillary block by constricting the pupil, pulling the peripheral iris away from the meshwork and reopening the angle. This is why it is a mainstay of acute attack treatment despite being obsolete for POAG.

Non-pupillary-block mechanisms also exist and are worth knowing:

• Plateau iris — anteriorly positioned ciliary processes push the peripheral iris forward; the central chamber is of normal depth and a patent iridotomy does NOT fully cure it (needs laser iridoplasty).
• Phacomorphic (lens-induced, an intumescent cataract) — technically a secondary angle closure.

Clinical features of an acute attack

A patient presents with a sudden, dramatic, painful red eye.

Symptoms:

• Severe ocular/peri-orbital pain and headache.
• Coloured haloes around lights (due to corneal epithelial oedema acting as a prism/diffraction grating).
• Sudden marked blurring of vision.
• Nausea and vomiting, abdominal pain (vagal) — can mimic an acute abdomen or migraine and is a classic trap.
• A history of prior intermittent episodes relieved by sleep (miosis during sleep breaks the block).

Signs (the examination triad set):

Sign	Finding	Mechanism
IOP	Very high, 40–80 mmHg; globe "stony hard"	Acute outflow block
Conjunctiva	Circumcorneal (ciliary) congestion, lid oedema	Ciliary flush
Cornea	Hazy/oedematous (epithelial bedewing)	Pressure overwhelms endothelial pump
Anterior chamber	Very shallow, aqueous flare	Iris bombé, ischaemia
Pupil	Fixed, mid-dilated, vertically oval, non-reacting	Iris sphincter ischaemia
Fellow eye	Shallow chamber / occludable angle	Bilateral predisposition

High-yield: A fixed, mid-dilated (semi-dilated), vertically oval, non-reacting pupil in a red painful eye with a rock-hard globe = acute angle-closure glaucoma until proven otherwise. The mid-dilated (not fully dilated, not constricted) pupil is the examiner's discriminator.

After an attack subsides, look for the residual stigmata of prior acute attack:

• Glaukomflecken — small anterior subcapsular grey-white lens opacities from focal epithelial necrosis (pathognomonic of a previous acute attack).
• Iris atrophy / spiral-shaped iris stromal atrophy and a fixed pupil.
• Sectoral iris sphincter palsy.

Investigations and the investigation of choice

PACG is largely a clinical and gonioscopic diagnosis.

• Gonioscopy — the investigation of choice / gold standard for assessing the angle. Performed on the fellow eye and, once the cornea clears, the affected eye. Indentation (dynamic) gonioscopy with a Zeiss/Sussman 4-mirror lens distinguishes appositional closure (opens on indentation) from synechial closure (PAS, stays shut).
  • Shaffer grading: Grade 0 = closed; Grade 1 = ≤10°, extremely narrow, likely to close; Grade 4 = 35–45°, wide open.
  • Van Herick technique (slit-lamp, no contact) estimates peripheral chamber depth as a ratio of the limbal anterior-chamber depth to corneal thickness — a quick screening for occludable angles.
• Applanation tonometry (Goldmann) for IOP.
• Anterior segment OCT / UBM (ultrasound biomicroscopy) — image the angle, plateau iris configuration, ciliary processes; UBM is best for retro-iridal structures.
• Slit-lamp — shallow chamber, oedematous cornea, mid-dilated pupil, Glaukomflecken.
• Optic disc & OCT RNFL / perimetry — to detect/document glaucomatous neuropathy (defines PACG vs PAC) once media clear.

High-yield: Gonioscopy is the single most important diagnostic test and is mandatory before any dilatation in a suspect eye. Never use a fundus-dilating drop in a clinically shallow, occludable angle without iridotomy.

Management of the acute attack

The aim is to rapidly lower IOP, clear the cornea, break pupillary block, and prevent fellow-eye attack, then deliver definitive laser/surgical treatment. This sequence is one of the most repeated exam questions.

Emergency medical sequence (flow):

1. Acetazolamide 500 mg IV (or oral) stat — carbonic anhydrase inhibitor, cuts aqueous production. DOC to start.
2. Topical β-blocker (timolol 0.5%) — reduces aqueous secretion.
3. Topical α2-agonist (apraclonidine/brimonidine) and topical steroid (prednisolone) to reduce inflammation.
4. Hyperosmotic agent — IV mannitol 20% (1–2 g/kg) or oral glycerol — for IOP not responding/extremely high; draws fluid out of the vitreous, deepens the chamber. (Avoid glycerol in diabetics; mannitol caution in cardiac/renal failure.)
5. Pilocarpine 2% — give after IOP starts to fall (when IOP is very high the iris sphincter is ischaemic and unresponsive to pilocarpine; once IOP drops it works to constrict the pupil and break the block). Often one drop, then repeat.
6. Analgesia and antiemetics for symptom control.

Drug class	Example	Action	Caution
Carbonic anhydrase inhibitor	Acetazolamide	↓ aqueous production	Sulpha allergy, hypokalaemia, renal stones
Hyperosmotic	Mannitol IV / glycerol PO	Dehydrates vitreous, ↓ volume	CCF, renal failure; glycerol raises blood sugar
Miotic	Pilocarpine 2%	Constricts pupil, opens angle	Ineffective at very high IOP; give after IOP falls
β-blocker	Timolol	↓ aqueous secretion	Asthma, bradycardia, heart block
α2-agonist	Brimonidine/apraclonidine	↓ secretion + ↑ uveoscleral outflow	Avoid in neonates/infants
Steroid	Prednisolone acetate	↓ inflammation	—

High-yield: Prostaglandin analogues (latanoprost) and pilocarpine timing are favourite traps. Pilocarpine is given AFTER IOP begins to fall because a sphincter ischaemic from very high pressure will not respond. Avoid systemic atropine/anticholinergics entirely.

Definitive treatment:

• Laser peripheral iridotomy (LPI) — the definitive cure for pupillary-block angle closure. A Nd:YAG laser creates a full-thickness hole in the superior peripheral iris (covered by the lid to reduce dysphotopsia), creating an alternate route for aqueous and equalising posterior/anterior chamber pressure → iris flattens → angle reopens.
• Prophylactic LPI to the fellow (unaffected) eye is mandatory — risk of an acute attack in the unoperated fellow eye is roughly 40–80% over 5–10 years.
• If the cornea is too hazy for LPI, surgical peripheral iridectomy or laser iridoplasty / paracentesis / lens extraction are alternatives.
• Lens extraction (clear-lens or cataract surgery) is increasingly first-line, especially with a cataractous/large lens (EAGLE trial supported lens extraction over LPI in PAC/PACG with raised IOP) — removing the bulky lens deepens the chamber and opens the angle.
• For plateau iris, add argon laser peripheral iridoplasty (LPI alone is insufficient).
• Established PACG with extensive synechiae/optic damage → ongoing medical IOP control and trabeculectomy (filtration surgery) if uncontrolled.

High-yield: Laser peripheral iridotomy is the definitive procedure for pupillary block; it is offered to BOTH eyes (treatment to affected, prophylaxis to fellow).

Complications

• Optic atrophy and irreversible blindness if IOP not controlled — the end-point of all glaucoma.
• Central retinal artery / vein occlusion during a severe attack from very high IOP.
• Cataract / Glaukomflecken from a prior attack.
• Permanent peripheral anterior synechiae (PAS) → chronic synechial angle closure even after LPI.
• Iris atrophy, corectopia, fixed dilated pupil, posterior synechiae.
• Malignant glaucoma (aqueous misdirection) — a feared post-iridotomy/post-surgery complication where aqueous is diverted posteriorly into the vitreous, shallowing the central chamber with a raised IOP and a patent iridotomy; treated with cycloplegics (atropine), aqueous suppressants, and sometimes vitrectomy — note this is the one situation where atropine helps.
• Chronic PACG progressing silently like POAG.

Key differentials of the acute red, painful eye

Condition	IOP	Pupil	Cornea/Discriminator
Acute PACG	Very high	Mid-dilated, fixed, oval	Hazy cornea, shallow chamber, haloes, hard globe
Acute anterior uveitis (iritis)	Normal/low (raised if trabeculitis)	Small/constricted, irregular	KPs, cells/flare, posterior synechiae, photophobia
Acute bacterial conjunctivitis	Normal	Normal, reactive	Discharge, no pain/halo, clear cornea, normal vision
Acute keratitis / corneal ulcer	Normal	Normal/small	Epithelial defect staining, FB sensation
Acute endophthalmitis	Variable	—	Hypopyon, post-surgical/trauma, profound vision loss
Scleritis	Normal	Normal	Deep boring pain, violaceous hue, tender globe

High-yield: The discriminator between acute PACG and acute iritis is the pupil — mid-dilated and fixed in PACG versus small and irregular in iritis. Both can be painful red eyes with circumcorneal congestion.

Recently asked / exam angle

• The "fixed, vertically oval, mid-dilated, non-reacting pupil" with a stony-hard eye — single-best-answer image/clinical vignette; pick acute angle-closure glaucoma.
• Mechanism question: Relative pupillary block as the cause; pupillary block is maximal at a semi-dilated pupil.
• Drug timing trap: Pilocarpine is added after IOP starts to fall (ischaemic sphincter); first-line is acetazolamide. Avoid PG analogues and atropine.
• Definitive treatment: Laser peripheral iridotomy; prophylactic LPI to fellow eye.
• Glaukomflecken — recognise as the sign of a previous acute attack (anterior subcapsular lens opacities).
• Predisposition: Hypermetropia + shallow chamber + Asian female (contrast with myopia in POAG).
• Precipitants: Dim light, mydriatics, stress, anticholinergics.
• EAGLE trial / clear lens extraction as first-line in PAC/PACG with raised IOP — newer postgraduate-level point.
• Plateau iris — chamber centrally normal, LPI insufficient, needs iridoplasty.
• Drug to avoid: Topical/systemic atropine, sympathomimetics, ipratropium — can precipitate an attack.
• Investigation of choice: Gonioscopy (indentation gonioscopy distinguishes appositional vs synechial closure).
• Van Herick / Shaffer grading and Glaukomflecken as one-word recall items.

Rapid revision

1. PACG = angle closure (iridotrabecular contact) plus glaucomatous optic neuropathy; angle closure without disc damage is PAC/PACS.
2. Dominant mechanism = relative pupillary block, maximal at a mid-dilated pupil.
3. Classic patient: hypermetropic, middle-aged, Asian female with a shallow anterior chamber (POAG = myopia).
4. Acute attack: painful red eye, haloes, hazy cornea, fixed mid-dilated oval pupil, stony-hard globe, IOP 40–80 mmHg, nausea/vomiting.
5. Gonioscopy is the investigation of choice; Shaffer grade 0 = closed angle; Van Herick screens chamber depth.
6. First drug = IV/oral acetazolamide; add timolol, brimonidine, steroid; mannitol for refractory high IOP.
7. Pilocarpine is given AFTER IOP starts to fall (ischaemic sphincter unresponsive at very high pressure); avoid prostaglandin analogues and atropine.
8. Laser peripheral iridotomy (Nd:YAG, superior iris) is the definitive treatment; prophylactic LPI to the fellow eye is mandatory.
9. Lens extraction (EAGLE trial) is increasingly first-line, especially with a thick/cataractous lens.
10. Glaukomflecken (anterior subcapsular lens opacities) = sign of a previous acute attack.
11. Plateau iris needs laser iridoplasty — LPI alone is insufficient; central chamber depth is normal.
12. Malignant glaucoma (aqueous misdirection) = shallow chamber + high IOP despite a patent iridotomy; treat with atropine/cycloplegics + aqueous suppressants ± vitrectomy.