Author: Claude (AI), from PubMed abstracts · Reviewed by: Dr Mina Abdelmseih · Reviewed: 2026-11-15 · Review due: 2027-11-15

Educational content only. Not personalised medical advice. Clinical decisions remain the responsibility of the treating clinician.

Acute Primary Angle Closure

Acute primary angle closure (APAC) is an eye emergency in which intraocular pressure (IOP) can reach 50 mmHg or more [S3]. Treatment aims to lower IOP within hours and then open the angle definitively, and in a 10-year follow-up of a randomised trial four eyes treated with laser iridotomy alone became blind [S6].

Key points - Medical therapy, anterior chamber paracentesis and laser iridoplasty are used in sequence to break the attack; in one RCT 92.20% of eyes were controlled by 6 hours with this approach [S12]. - Immediate paracentesis lowered IOP faster and gave better visual acuity than medical treatment alone in a small RCT [S3]. - In eyes with APAC and cataract, early phacoemulsification gave better IOP control than laser peripheral iridotomy (LPI) at 2 years [S2] and less medication, fewer synechiae and less blindness at 10 years [S6]. - Topiramate can cause acute angle closure, with onset peaking about 2 weeks after starting the drug; stopping it plus medical therapy resolved most cases [S9]. - When medicine fails, phacoemulsification with goniosynechialysis (phaco-GSL) and phacotrabeculectomy both controlled IOP in a Vietnamese multicentre RCT, with fewer complications after phaco-GSL [S7].

Evidence last checked: 2026-10-17 (PubMed abstracts).

Red flags

• IOP of 50 mmHg or more with reduced vision and pain [S3].
• Corneal oedema, ciliary flush and a non-reactive pupil [S3] [S5].
• Attack not controlled by medical therapy (refractory APAC): surgery is needed [S7] [S10].
• A patient started on topiramate in the last weeks who develops eye symptoms: in reported cases the mean time to onset was 14.1 days [S9].
• Recent pupil dilation in an eye with narrow angles: 0.64% of narrow-angle subjects developed acute angle closure within 6 hours of tropicamide despite oral acetazolamide [S1].

Recognise it: features and risk factors

• Symptoms and signs measured in trials include pain, reduced visual acuity, corneal oedema, conjunctival erythema, ciliary flush and photophobia [S3] [S5].
• Anatomy. Primary angle-closure glaucoma is associated with a shallower anterior chamber, shorter axial length, more hyperopic refraction and cataract (OR 3.77) [S11].
• Drugs. Short-term antidepressant exposure was associated with acute angle closure (OR 1.36) [S11]. Topiramate-induced cases were mostly women (75.3%) with a mean age of 34.88 years, usually treated for migraine [S9]. These patients were younger than those in APAC trials (mean age 66.0 years in [S2]) [S9].
• Dilation. The risk of an acute attack after dilation with tropicamide in Asian narrow-angle subjects was low (0.64%), and a narrower gonioscopic angle was the only clinical predictor of an IOP rise [S1].

Confirm it

• Measure IOP; trials used Goldmann applanation tonometry and gonioscopy [S1] [S2].
• Examine the fellow eye; narrow angles on gonioscopy predict IOP rise after dilation [S1].
• Anterior segment OCT shows the angle widening after treatment and is a research tool for comparing treatments [S4]. It is not required to make the diagnosis.

Manage it

Before acting on this section, check the national and local guidelines, product information and regulatory approvals that apply where you practise. See the medical disclaimer.

Tier A (primary care / no specialist)

• Recognise the red flags and refer immediately to an eye unit.
• If the patient takes topiramate, the drug was stopped in every reported case of topiramate-induced closure [S9]; contact the prescriber.
• Dosing of IOP-lowering drugs is not covered by these sources; follow local formularies and protocols.

Tier B (general eye clinic)

1. Medical therapy first. Systemic carbonic anhydrase inhibitors, hyperosmotic agents and steroids were used alongside topical therapy in 66.2% of topiramate cases [S9]. In one RCT, adding a single dose of timolol to sequential treatment did not improve IOP reduction, remission rate or time to relief [S12].
2. Subconjunctival dexamethasone. Adding 2.5 mg subconjunctival dexamethasone (as reported in [S5]) to standard drugs gave lower IOP at 24 hours and a higher 24-hour success rate (79.7% vs 54.9%), with less ciliary flush and pain, in an RCT of 42 patients [S5].
3. Anterior chamber paracentesis. In an RCT of eyes with IOP of 50 mmHg or more, paracentesis plus medical treatment lowered IOP faster at 15 minutes to 1 hour, reduced pain at 1 to 2 hours and gave better final visual acuity (0.43 vs 0.74 logMAR) [S3].
4. Laser iridoplasty. Argon laser peripheral iridoplasty widened the angle more than medical therapy at 1 hour in a randomised study of 30 patients [S4]. In a sequential protocol of drugs, paracentesis and iridoplasty, 91.46% to 92.20% of eyes were controlled at 6 hours [S12].
5. Laser peripheral iridotomy. After LPI, an IOP spike at 1 hour occurred in 6% to 9.8% of eyes; a review recommends checking IOP at 1 hour in patients with hyphaema, pigment dispersion, high pre-treatment IOP, thick irides or optic nerve damage [S8].

Tier C (specialist centre)

• APAC with cataract. Phacoemulsification within 1 week gave 2-year IOP control survival of 89.5% vs 61.1% with LPI [S2]. At 10 years, the phaco group used less medication, had less synechial closure and had no blindness, against 4 blind eyes in the LPI group [S6].
• Refractory APAC with cataract. Phaco-GSL and unaugmented phacotrabeculectomy both controlled IOP at 1 year, but complications in the first 3 months were 14.3% vs 62.2%, and visual acuity was better after phaco-GSL [S7].
• Refractory APAC without significant cataract. Laser iridoplasty followed by surgical iridectomy and trabeculectomy gave similar 1-year success (97.1% vs 92.6% complete success), with more early complications after iridoplasty plus iridectomy (45.9% vs 33.3%) [S10].

Refer when

Pitfalls

• Relying on extra timolol to rescue a failing protocol [S12].
• Treating APAC with cataract by LPI alone and not offering lens extraction [S2] [S6].
• Missing drug causes such as topiramate in young patients [S9] or antidepressants [S11].
• Skipping the 1-hour IOP check after LPI in eyes with risk factors [S8].

Evidence notes

• All trials are small and single-country, mostly East and Southeast Asian; generalisability to other populations is limited [S8].
• The 10-year follow-up examined only 64.5% of patients, and 71.4% of the LPI group had already had lens extraction [S6].
• The topiramate evidence is case reports only [S9]; the antidepressant link is observational [S11].
• Not covered by these sources: doses and choice of acetazolamide, mannitol, glycerol and pilocarpine; time windows for transfer; management of the fellow eye; non-pupillary-block mechanisms.

Related articles

• Primary Angle-Closure Disease: Suspects to Glaucoma
• Gonioscopy and anterior-segment imaging of the angle
• The red eye: triage

References

See the numbered source list below. Each marker [S#] links to its PubMed and DOI record.