Summary

Acute Angle Closure Glaucoma (AACG) is an ophthalmic emergency caused by the sudden obstruction of aqueous humour outflow at the iridocorneal angle. This leads to a rapid and severe rise in Intraocular Pressure (IOP), often >50 mmHg (Normal <21 mmHg). The high pressure causes ischaemia of the optic nerve and can lead to permanent blindness within hours if untreated. It classically presents with a painful red eye, blurred vision with haloes, and systemic symptoms like nausea and vomiting. Management involves immediate medical therapy to lower pressure (Acetazolamide, Pilocarpine, Beta-blockers) followed by definitive laser treatment (YAG Peripheral Iridotomy) to bypass the blockage.

Key Facts

• Mechanism: Pupil block. The iris pushes forward, closing the drainage angle.
• Target IOP: Normal is 10-21 mmHg. In AACG, it can hit 60-80 mmHg.
• Prophylaxis: The other eye is at extremely high risk (50% in 5 years). It must be treated prophylactically with laser.
• Refractive Error: Strongly associated with Hypermetropia (Long-sightedness) because these eyes are physically smaller and crowded.

Clinical Pearls

"The Great Mimic": Patients often present with severe headache and vomiting. They may be misdiagnosed as Migraine, Meningitis, or Gastroenteritis. Always check the red reflex and feel the eye (rock hard) in any patient with headache + vomiting.

"Haloes": The high pressure forces fluid into the corneal stroma (oedema). This acts like a prism, splitting light into rainbows or haloes around streetlights.

"Mid-Dilated Pupil": The high IOP causes ischaemia of the iris sphincter muscle. It gets stuck halfway (neither constricted nor dilated). It is usually vertically oval.

"Acetazolamide First": Drops might not work initially because the iris vessels are compressed by pressure (so the drug isn't absorbed). Systemic Acetazolamide (IV/Oral) helps "break" the pressure first.

        ACUTE RED EYE + PAIN + HALOES
                     ↓
          CHECK IOP (High) + ANGLE
                     ↓
           IMMEDIATE MEDICAL THERAPY
  ("The Kitchen Sink" - throw everything at it)
                     ↓
      1. SYSTEMIC: IV Acetazolamide 500mg
      2. TOPICAL:  Timolol (Beta-blocker)
                   Apraclonidine (Alpha-2)
                   Pilocarpine (Miotic)
                   Prednisolone (Steroid)
                     ↓
           RE-CHECK IOP AT 1 HOUR
                     ↓
             FALLING? CORNEA CLEAR?
           ┌─────────┴─────────┐
          YES                 NO (Resistant)
           ↓                   ↓
  YAG LASER PERIPHERAL    OSMOTIC AGENTS
  IRIDOTOMY (PI)          (IV Mannitol)
  (Curative)                   ↓
                          SURGERY (Trab)

1. Medical Therapy (Immediate)

• Acetazolamide (Diamox): Carbonic Anhydrase Inhibitor. Reduces aqueous production. IV 500mg STAT.
• Topical Drops:
  • Pilocarpine (2-4%): Parasympathomimetic. Constricts pupil -> Pulls iris away from angle. Intensive (every 15 mins). Note: May not work if IOP >50 due to iris ischaemia.
  • Timolol (0.5%): Beta-blocker. Reduces production.
  • Apraclonidine (1%): Alpha-agonist. Reduces production + Increases outflow.
  • Prednisolone: Reduces inflammation.

2. Physical Measures

• Examples: Lie patient flat (Supine). Why? The lens falls back slightly, potentially opening the angle.

3. Laser Therapy (Definitive)

• YAG Peripheral Iridotomy (PI):
  • A laser creates a small hole in the peripheral iris.
  • Allows aqueous to flow directly from posterior to anterior chamber, bypassing the pupil block.
  • The iris falls back, opening the angle.
  • Prophylaxis: The contralateral eye MUST be treated (usually at a later date).

YAG Peripheral Iridotomy (PI)

1. Drop: Pilocarpine (to stretch iris and make it thin).
2. Lens: Abraham contact lens placed on eye (magnifies iris).
3. Target: Superior Iris (covered by lid usually) or 10 o'clock/2 o'clock. Ideally in a "crypt" (thin spot).
4. Shot: Nd:YAG laser burst.
5. Success: "Pigment plume" seen. Flow of fluid confirms patency.

Trabeculectomy (The "Trab")

• Indications: Failed PI, Chronic Glaucoma.
• Concept: Creating a "trapdoor" in the sclera to let fluid leak out under the conjunctiva (forming a "Bleb").
• Steps:
  • Conjunctival flap.
  • Scleral trapdoor cut.
  • Punch hole in excessive tissue (Sclerostomy).
  • Iridectomy (hole in iris).
  • Closure: Loose sutures allow controlled leak.
• Anti-Metabolites: Mitomycin C used to prevent scarring (failure).

Shaffer Grading System (Estimated angle in degrees).

EAGLE Trial (2016)

• Compared Clear Lens Extraction (Cataract surgery) vs Laser PI for Primary Angle Closure.
• Result: Early Cataract Surgery was SUPERIOR to Laser PI.
• Reason: Removing the big lens creates huge space, curing the crowding forever.
• Practice Change: We now consider early cataract surgery for angle closure patients.

NICE NG81

• Refer immediately (same day).
• Offer Laser PI to affected and contralateral eye.

What is Acute Glaucoma?

The eye is filled with fluid that usually drains away gradually. In this condition, the drain (the angle) suddenly blocks. It's like putting a plug in a sink with the tap running. The pressure builds up rapidly.

Why does it hurt?

The eye is a sealed ball. When the pressure spikes, it stretches the wall of the eye and the nerves, causing agonising pain and sickness.

How do you treat it?

1. Drugs: We give you a cocktail of drops and an injection to turn down the tap (stop fluid production) and open the drain.
2. Laser: Once the pressure is down, we use a laser to make a microscopic safety valve (hole) in the iris. This prevents it from blocking again.

Will I lose my sight?

If treated quickly (within hours), sight usually returns. If left too long, the pressure kills the optic nerve, causing permanent blindness. This is why you must come to A&E immediately.