ACUTE ANGLE-CLOSURE GLAUCOMA (AACG)

10-Mark University Examination Notes

1. DEFINITION

2. ETIOLOGY

• Hypermetropic (short, small) eye with shallow anterior chamber
• Short axial length (nanophthalmos - axial length <20 mm carries highest risk)
• Thick, anteriorly placed crystalline lens
• Narrow drainage angle (iridocorneal angle)
• Shallow anterior chamber depth
• Large lens-to-eye volume ratio

• Pharmacological mydriasis (atropine, tropicamide, sympathomimetics)
• Watching TV/reading in a darkened room
• Emotional stress, prolonged semi-prone position
• Systemic medications: anticholinergics, antihistamines, cold/flu remedies, topiramate and sulfa derivatives (cause ciliary body effusion), motion-sickness patches

• Age: average onset ~62 years
• Female sex (more commonly affected)
• Asian/East Asian and Indian race (highest global burden)
• Family history of angle closure
• Hypermetropia >1 dioptre

3. PATHOGENESIS

Diagram: Mechanism of Pupillary Block

NORMAL EYE                          ACUTE ANGLE CLOSURE
                                    
  Cornea                              Cornea (oedematous)
    |                                   |
 Open angle                         Closed angle
  /    \                               / \
Iris  Trabeculum                   Iris bowed   Blocked
 |      |                          forward      trabeculum
 |   Aqueous                         |
Lens  flows freely              Iris-lens contact
                                 (pupillary block)
                                    ↑ IOP

1. Relative pupillary block: At mid-dilation (~4 mm), the iris is in maximal contact with the anterior lens surface, creating resistance to aqueous flow from the posterior chamber through the pupil to the anterior chamber.
2. Posterior chamber pressure rise: Aqueous accumulates behind the iris, raising posterior chamber pressure above anterior chamber pressure.
3. Iris bombe: The pressure difference pushes the peripheral iris anteriorly (iris bombe configuration), causing the iris to bow forward like a sail.
4. Iridotrabecular contact (ITC): The bowed peripheral iris makes contact with and occludes the trabecular meshwork, the primary outflow pathway for aqueous.
5. IOP spike: With outflow blocked, aqueous accumulates and IOP rises acutely to 50-80 mmHg.
6. Ischaemic damage: Extreme IOP causes ischaemia to the iris sphincter, corneal endothelium, and optic nerve head - all within hours.

Diagram: Aqueous Flow in Normal vs. Angle Closure

                    NORMAL                     ANGLE CLOSURE
    ┌──────────────────────┐     ┌────────────────────────────┐
    │   Ciliary processes  │     │    Ciliary processes       │
    │        ↓             │     │          ↓                 │
    │   Posterior chamber  │     │   Posterior chamber        │
    │        ↓ (pupil)     │     │   ↑ pressure (blocked)     │
    │   Anterior chamber   │     │   IRIS BOMBE ←──────────── │
    │        ↓             │     │   Peripheral iris blocks   │
    │   Trabecular meshwork│     │   trabeculum               │
    │        ↓             │     │        ✗                   │
    │   Schlemm's canal    │     │   IOP ↑↑ (50-80 mmHg)      │
    └──────────────────────┘     └────────────────────────────┘

4. CLINICAL FEATURES

Symptoms

• Sudden severe unilateral eye pain (may radiate to forehead, temple, jaw)
• Dramatic decrease in vision (VA typically 6/60 to hand movements)
• Coloured haloes around lights - from corneal epithelial oedema
• Nausea and vomiting (can dominate, causing misdiagnosis as acute abdomen)
• Headache, photophobia

Signs (Classic Triad: Red eye + Hazy cornea + Mid-dilated pupil)

Clinical photograph from Kanski's - Acute primary angle closure:

Late/Resolved Signs

• Glaukomflecken: white foci of anterior lens capsule/cortex necrosis (pathognomonic of past attack)
• Iris atrophy with spiral-like configuration
• Irregular pupil, posterior synechiae
• Optic disc pallor + cupping (glaucomatous atrophy)

5. INVESTIGATIONS

1. Tonometry (Goldmann applanation) - confirms high IOP (50-80 mmHg)
2. Gonioscopy - shows closed angle (Grade 0-1 Shaffer); iridotrabecular contact; peripheral anterior synechiae (PAS); performed after attack subsides
3. Slit lamp examination - corneal oedema, shallow AC, flare, iris changes, glaukomflecken
4. Visual acuity - markedly reduced
5. Anterior segment OCT (AS-OCT) - images anterior chamber depth, iris profile, angle anatomy without contact
6. Ultrasound biomicroscopy (UBM) - shows plateau iris configuration, ciliary body position, narrow angle
7. Fundoscopy - optic disc congestion/oedema acutely; later pallor and cupping
8. Visual field testing - generalized depression acutely; if chronic component: inferior altitudinal loss, arcuate defects
9. B-scan ultrasonography - in atypical cases to exclude secondary causes
10. Biometry - if lens extraction is considered as definitive treatment

6. MANAGEMENT

Emergency/Immediate (Break the Attack)

• IV Mannitol 20% at 1-2 g/kg over 1 hour (hyperosmotic agent)
• Oral glycerol 50% (1 g/kg) or isosorbide
• Central corneal indentation (squint hook) to mechanically force aqueous into angle
• Topical 50% glycerol to clear corneal oedema for better visualization
• Early laser iridotomy/iridoplasty once oedema clears

Definitive Treatment

• Performed bilaterally (fellow eye has occludable angle)
• Creates a full-thickness hole in peripheral iris
• Allows aqueous to bypass pupillary block directly from posterior to anterior chamber
• Performed once the attack is broken (clear cornea, preferably normal IOP)
• Nd:YAG laser or argon laser

• Pilocarpine 2% four times daily (affected eye) + 1% four times daily (fellow eye)
• Topical steroid four times daily if acutely inflamed
• Timolol 0.5% twice daily, apraclonidine 1% three times daily, acetazolamide 250 mg four times daily as needed

• Peripheral iridectomy (surgical iridotomy)
• Lens extraction (clear lens extraction) - definitive, also deepens AC
• Goniosynechialysis - break down PAS
• Trabeculectomy - if significant angle damage with residual high IOP
• Cyclodiode laser (ciliary body ablation) in refractory cases

Diagram: Laser Peripheral Iridotomy

  BEFORE LPI                         AFTER LPI
                                    
   Iris bombe                       Flat iris
   (bowed forward)                  (decompressed)
        ↑                               
   Aqueous trapped                  Aqueous bypasses pupil
   behind iris                      through iridotomy hole
                                         ↓
   Angle closed ✗                   Angle opens ✓
   IOP ↑↑                          IOP normalizes

7. VISUAL FIELD CHANGES IN AACG

• During acute attack: generalized constriction of visual field due to corneal oedema and extreme IOP elevation
• After resolution: if optic nerve damage has occurred - inferior altitudinal defect (most common), arcuate scotoma, or generalized depression
• Severe/prolonged attack: can result in profound visual loss with only a small central island remaining or complete blindness

8. COMPLICATIONS

PRIMARY OPEN-ANGLE GLAUCOMA (POAG)

10-Mark University Examination Notes

1. DEFINITION

• Retinal nerve fibre layer (RNFL) thinning
• Glaucomatous optic nerve head damage (increased cup-to-disc ratio)
• Characteristic progressive visual field loss
• Open anterior chamber angle on gonioscopy
• No secondary cause for the optic neuropathy

2. ETIOLOGY

Primary Risk Factors

Genetic Factors

• MYOC gene mutation (myocilin - found in trabecular meshwork)
• OPTN gene mutation (optineurin)
• At least 127 loci associated with POAG in genome-wide association studies

Other Risk Factors

• Vascular disease (systemic hypertension, cardiovascular disease, migraine/vasospasm)
• Translaminar pressure gradient (difference between IOP and CSF pressure)
• Systemic calcium-channel blockers (meta-analysis: higher glaucoma prevalence)
• Diabetes mellitus (association less clear-cut)
• Anti-VEGF therapy (sustained IOP elevation, especially bevacizumab, after recurrent injections)

3. PATHOGENESIS

A. Mechanical Theory

HIGH IOP  →  Lamina cribrosa deformation
         →  Compression/distortion of axon bundles
         →  Axoplasmic flow obstruction
         →  Retinal ganglion cell (RGC) death
         →  RNFL thinning
         →  Optic cup enlargement (glaucomatous cupping)
         →  Visual field defects

B. Vascular Theory

Trabecular Meshwork Dysfunction

• Accumulation of extracellular matrix in trabecular beams
• Loss of trabecular endothelial cells
• Increased stiffness of trabecular meshwork (MYOC mutations)
• Oxidative damage to trabecular cells

Diagram: Pathogenesis of POAG

Trabecular meshwork dysfunction
         ↓
   Increased aqueous outflow resistance
         ↓
   ELEVATED IOP (or normal IOP + vascular insufficiency)
         ↓
   Lamina cribrosa deformation  +  Optic nerve head ischaemia
         ↓
   Retinal ganglion cell (RGC) axon damage/death
         ↓
   Retinal nerve fibre layer (RNFL) thinning
         ↓
   Optic disc cupping (vertical C/D ratio ↑, rim thinning)
         ↓
   Visual field defects (arcuate, nasal step, tunnel vision)
         ↓
   Blindness (if untreated)

4. CLINICAL FEATURES

Symptoms

• Usually none in early-to-moderate disease
• Patients typically present incidentally (routine refraction, screening)
• Late: blurred vision, reduced peripheral vision
• Central vision is preserved until very late stage

Signs

• Usually >21 mmHg (though may be normal in normal tension glaucoma)
• Diurnal variation: highest in morning

NORMAL DISC              GLAUCOMATOUS DISC
                         
  ┌────────────┐          ┌────────────┐
  │  Rim (pink)│          │ ↑ Cup      │
  │  ┌──────┐  │          │  ┌──────┐  │  ← Thinned rim
  │  │ Cup  │  │          │  │Large │  │
  │  │ small│  │          │  │cup   │  │
  │  └──────┘  │          │  └──────┘  │
  └────────────┘          └────────────┘
  C/D ratio ~0.3          C/D ratio >0.6, asymmetry >0.2

• Increased cup-to-disc (C/D) ratio (>0.6 suspicious; >0.7 significant; asymmetry >0.2 significant)
• ISNT rule violated: Inferior > Superior > Nasal > Temporal rim thickness (normal order) - glaucoma causes preferential inferior and superior rim thinning
• Notching of the neuroretinal rim (typically inferotemporal or superotemporal)
• Disc haemorrhage (Drance haemorrhage) - splinter haemorrhage at disc margin; indicates progression, especially in NTG
• Bayonetting of blood vessels at disc margin
• Nasal shifting of vessels (vessels appear to emerge from the nasal side of the enlarged cup)
• RNFL defects - wedge-shaped darkening seen with red-free illumination

• Normal-depth anterior chamber
• Open angle on gonioscopy (Grade 3-4 Shaffer)
• Normal cornea
• IOP usually elevated (10-21 mmHg normal; >21 suspicious)

5. VISUAL FIELD CHANGES (Glaucomatous Visual Field Defects)

Diagram: Progressive Visual Field Loss in POAG

STAGE 1 - Early              STAGE 2 - Moderate
┌─────────────────┐          ┌─────────────────┐
│     Normal      │          │  Arcuate scotoma │
│       ●blind    │          │  ██████████●    │
│       spot      │          │  ██ (Bjerrum)   │
│                 │          │  Nasal step     │
└─────────────────┘          └─────────────────┘
Small paracentral             Arcuate defect from
depressions (superonasal)     10°-20° of fixation;
or nasal step                 Nasal step (bounded
                              by horizontal midline)

STAGE 3 - Advanced           STAGE 4 - End Stage
┌─────────────────┐          ┌─────────────────┐
│ █████████████  │          │     ████████████│
│ ████ Ring  ████│          │   ███ Temporal  │
│ ████scotoma████│          │   ███ island    │
│ █████████████  │          │   (no nasal     │
│      Small     │          │    field)       │
│   central area │          └─────────────────┘
└─────────────────┘          
Ring (annular) scotoma

Named Visual Field Defects in POAG

6. INVESTIGATIONS

1. Tonometry (Goldmann applanation) - IOP measurement; check diurnal curve
2. Corneal pachymetry (CCT) - thin cornea (<520 µm) is independent risk factor; thick cornea may give falsely elevated IOP
3. Gonioscopy - confirms open angle; grades angle width (Shaffer Grade 3-4)
4. Optic disc evaluation - slit lamp biomicroscopy (78D/90D lens) or stereoscopic disc photography; assess C/D ratio, rim, notching, disc haemorrhage
5. Visual field testing - Standard Automated Perimetry (SAP, Humphrey Field Analyzer); frequency doubling technology (FDT); detects and monitors progression
6. OCT (Optical Coherence Tomography) - quantifies RNFL thickness (superior and inferior poles most sensitive); ganglion cell complex (GCC); detects pre-perimetric changes; monitors progression
7. Heidelberg Retinal Tomography (HRT) - 3D optic disc imaging; Moorfields regression analysis
8. GDx VCC (Scanning Laser Polarimetry) - RNFL analysis with variable corneal compensation
9. Colour fundus photography - disc documentation; RNFL defects with red-free filter
10. Blood pressure measurement - to calculate ocular perfusion pressure

7. MANAGEMENT

Target IOP (Key Concept)

Step 1: Medical Therapy (First-line)

Step 2: Laser Therapy

• Selective Laser Trabeculoplasty (SLT) - selectively targets trabecular meshwork pigmented cells; 40-50 spots at 180° or 360°; can repeat; comparable to medication for initial therapy (LiGHT trial)
• Argon Laser Trabeculoplasty (ALT) - older technique, same principle

Step 3: Surgical Therapy

• Trabeculectomy (guarded filtration surgery) - creates a surgical fistula from anterior chamber to subconjunctival space (filtering bleb); most common glaucoma surgery; mitomycin C (MMC) used to prevent scarring
• Glaucoma drainage devices (tube shunts) - Ahmed, Baerveldt, or Molteno valves; for refractory/complex cases
• Minimally Invasive Glaucoma Surgery (MIGS) - iStent, Hydrus, OMNI (for mild-moderate disease combined with cataract surgery)
• Cyclodiode laser - transscleral ciliary body ablation for refractory glaucoma

Diagram: Trabeculectomy

          Conjunctiva
          Sclera
    ┌─────────────────────┐
    │   FILTERING BLEB    │  ← aqueous collects here subconjunctivally
    └────────┬────────────┘
             │ fistula
    ┌────────▼────────────┐
    │  Anterior chamber   │  ← aqueous drains from here
    │  (IOP reduced)      │
    └─────────────────────┘
    Scleral flap + sclerectomy + peripheral iridectomy

8. COMPLICATIONS

Complications of Untreated POAG

Complications of Treatment

COMPARATIVE TABLE: AACG vs. POAG