The eye requires a constant flow of fluid (Aqueous Humour) to maintain shape and nourish the lens/cornea.

The Flow Cycle

1. Production: Ciliary Body (behind the iris) secretes aqueous.
2. Transit: Flows through the pupil into the Anterior Chamber.
3. Drainage:
   • Trabecular Meshwork (90%): The primary drain. Located at the "Angle" where iris meets cornea. Drains into Schlemm's Canal -> Episcleral Veins.
   • Uveoscleral Outflow (10%): Seeps through the ciliary body muscle face. (Target of Latanoprost).

The Pressure Equation

• IOP = (Production / Outflow) + Venous Pressure
• Glaucoma is almost always a problem of OUTFLOW RESISTANCE.
• Cup-to-Disc Ratio:
  • The optic nerve head (Disc) has a central pit (Cup).
  • High pressure kills nerve fibers at the rim, making the Cup bigger.
  • Normal: 0.3
  • Glaucoma: >0.5 or Asymmetric (0.3 in left, 0.7 in right).

Classification by Mechanism

• Open Angle: The drain is accessible, but the filter is clogged (Microscopic resistance).
• Closed Angle: The iris is plastered against the cornea, physically covering the drain (Macroscopic block).

Epidemiology & Risk Factors

• Age: Risk rises sharply >40.
• Race: 4-6x higher in Black/African-Caribbean descent (onset is earlier and more aggressive).
• Family History: 1st degree relative = 4-9x risk.
• Myopia: Short-sighted eyes are longer, more susceptible to pressure damage.
• Diabetes: Increases risk.

Clinical Progression

1. Asymptomatic Phase: IOP 22-30. No vision loss yet.
2. Early Loss: Peripheral nasal step scotoma. Patient unaware (binocular vision compensates).
3. Advanced Loss: Arcuate scotoma (Bjerrum). "Tunnel Vision".
4. Terminal: Temporal island of vision remains. Finally, total blindness.

Diagnosis

1. Tonometry: IOP >21 mmHg (Normal 10-21).
2. Fundoscopy: "Cupping" of Optic Disc (Cup:Disc ratio >0.5).
3. Visual Fields: Arcuate scotoma (Bjerrum's area).
4. Gonioscopy: Confirms angle is OPEN.

Management Algorithm (POAG)

┌─────────────────────────────────────────────────────────────────────────────┐
│                    POAG MANAGEMENT LADDER                                   │
├─────────────────────────────────────────────────────────────────────────────┤
│   GOAL: Reduce IOP to prevent further nerve damage.                         │
│   (Cannot reverse existing damage).                                         │
│                                                                             │
│   1. PHARMACOLOGY (Eye Drops)                                               │
│   • **1st Line: Prostaglandin Analogues (Latanoprost)**.                    │
│     - Increases uveoscleral outflow. Once daily (Night).                    │
│     - S/E: Long eyelashes, darker iris, red eye.                            │
│   • **2nd Line: Beta Blockers (Timolol)**.                                  │
│     - Reduces production.                                                   │
│     - C/I: Asthma / Heart Block.                                            │
│   • **3rd Line: Carbonic Anhydrase Inhibitors (Dorzolamide)**.              │
│   • **4th Line: Alpha-2 Agonists (Brimonidine)**.                           │
│   └─────────────────────────────────────────────────────────────────────┘   │
│                          ↓                                                  │
│   2. LASER THERAPY (SLT)                                                    │
│   • **Selective Laser Trabeculoplasty (SLT)**.                              │
│   • Zaps the meshwork to stimulate better drainage.                         │
│   • NICE 2022 now recommends this as FIRST LINE option over drops.          │
│   └─────────────────────────────────────────────────────────────────────┘   │
│                          ↓                                                  │
│   3. SURGERY (Trabeculectomy)                                               │
│   • Creates a "trapdoor" valve for fluid to escape under conjunctiva.       │
│   • Forms a "bleb".                                                         │
│   • For advanced disease unmanageable with drops/laser.                     │
│   └─────────────────────────────────────────────────────────────────────┘

Pathophysiology

• The drainage angle is CLOSED physically by the iris bulging forward against the cornea.
• Precipitated by Pupil Dilation (Dark room / Stress / Anticholinergic drugs).
• The bunched up iris blocks the meshwork.

Clinical Features (EMERGENCY)

1. Severe Pain: Eye and Headache.
2. Red Eye: Ciliary flush.
3. Haloes: Seeing rainbows around streetlights (due to corneal edema).
4. Nausea/Vomiting: Vagal response to pain.
5. Semi-dilated Pupil: Fixed, non-reactive oval pupil.
6. Hard Eye: Rock hard on palpation.

Image: Acute Glaucoma Eye

Management Algorithm (AACG Emergency)

┌─────────────────────────────────────────────────────────────────────────────┐
│                    AACG EMERGENCY PROTOCOL                                  │
├─────────────────────────────────────────────────────────────────────────────┤
│   IMMEDIATE ACTION (Sight Saving)                                           │
│   • Patient lying flat (opens angle).                                       │
│   • Call Ophthalmologist immediately.                                       │
│   └─────────────────────────────────────────────────────────────────────┘   │
│                          ↓                                                  │
│   1. MEDICAL THERAPY (To drop pressure rapidly)                             │
│   • **IV Acetazolamide** 500mg (Stops production).                          │
│   • **Topical Pilocarpine** (Constricts pupil -> pulls iris away from       │
│     angle).                                                                 │
│   • **Topical Beta-blocker / Alpha-agonist**.                               │
│   └─────────────────────────────────────────────────────────────────────┘   │
│                          ↓                                                  │
│   2. DEFINITIVE TREATMENT (Laser)                                           │
│   • **YAG Laser Iridotomy (PI)**.                                           │
│   • Shoots a tiny hole in the iris to create a bypass channel.              │
│   • PERFORM ON BOTH EYES (Prophylactic on the other eye).                   │
│   └─────────────────────────────────────────────────────────────────────┘

• Screening recommended for >40s, especially with family history.
• Ethnicity:
  • POAG common in Afro-Caribbean.
  • AACG common in Asian (smaller eyes, shallower angles).

• POAG: Must notify DVLA IF usually both eyes affected or severe field loss.
• Visual Field Test (Esterman) required.

Exam-Focused Points

1. Timolol & Asthma: The classic exam trap. Beta-blocker drops are absorbed systemically. Can precipitate asthma attack.
2. Latanoprost Side Effects: Increased eyelash length, iris pigmentation change (brown).
3. AACG Triad: Painful Red Eye + Haloes + Fixed Pupil.
4. Avoid Mydriatics: Never dilate the pupil (Atropine/Tropicamide) in someone with shallow angles -> precipitates AACG.
5. Normal Tension Glaucoma: You can have glaucoma damage with "Normal" IOP (usually driven by poor blood supply).

Common Exam Scenarios

• 70yo Asian woman, entering dark cinema, sudden eye pain and vomiting. (AACG).
• Asthmatic patient with Glaucoma. Which drop to avoid? (Timolol).
• African man, 50, routine optician check finds IOP 24. No symptoms. (POAG).

What is Glaucoma?

"Think of your eye like a sink with a tap always running (producing fluid) and a drain (removing fluid). In Glaucoma, the drain is blocked. The sink fills up, pressure builds, and this pressure crushes the optic nerve at the back, causing blindness."

Can I get my vision back?

"No. The nerve damage is permanent. The treatment is purely to LOWER the pressure to prevent further loss. This is why using your drops every day is crucial, even if you feel fine."

Key Guidelines

Evidence-Based Recommendations