GLAUCOMA - Comprehensive Study Notes

Reference: AK Khurana - Comprehensive Ophthalmology (note: AK Khurana's textbook is not available in the library database; these notes are compiled from Kanski's Clinical Ophthalmology 10th Edition - the internationally equivalent standard reference - with content structured to match the AK Khurana syllabus outline for ophthalmology)

1. DEFINITION

• It is an optic neuropathy, not simply "raised IOP"
• Intraocular pressure (IOP) is the most important modifiable risk factor (normal IOP = 10-21 mmHg)
• Optic nerve damage causes retinal nerve fibre layer (RNFL) thinning
• Results in characteristic visual field loss - typically starts peripherally and progresses centrally
• The anterior chamber angle may be open (most common) or closed

2. TYPES OF GLAUCOMA

A. Primary Glaucoma

1. Primary Open-Angle Glaucoma (POAG)

• Most common type in White and Black populations
• Chronic, progressive optic neuropathy of adult onset
• Anterior chamber angle is open on gonioscopy
• IOP is elevated due to increased resistance to aqueous outflow through the trabecular meshwork
• Asymptomatic in early stages - visual field loss is not noticed until significant damage has occurred
• Both eyes affected, though asymmetrically

• Raised IOP (most important)
• Age (>40 years)
• Race (4x more common in Black people; more severe)
• Family history (4x risk in siblings, 2x in offspring)
• Myopia
• Vascular disease (systemic hypertension, cardiovascular disease)
• Large optic disc
• Low ocular perfusion pressure

2. Primary Angle-Closure Glaucoma (PACG)

• More common in Asian and Inuit populations
• Anterior chamber angle is narrow or closed - iris blocks the trabecular meshwork
• Mechanism: pupillary block - aqueous cannot pass from posterior to anterior chamber - iris bows forward (iris bombe)
• More common in: hypermetropes, shallow anterior chambers, small eyes, female sex, advancing age

• Acute PACG - sudden, painful, dramatic onset (see clinical features below)
• Sub-acute (intermittent) PACG - recurrent episodes, self-limiting
• Chronic PACG - gradual angle closure, mimics POAG in presentation

3. Primary Congenital / Developmental Glaucoma

• Present at birth or develops within first few years of life
• Due to trabeculodysgenesis (maldevelopment of trabecular meshwork)
• Buphthalmos (ox-eye) - enlarged globe due to raised IOP in the elastic sclera of infants
• Triad: buphthalmos, epiphora (tearing), photophobia

B. Secondary Glaucoma

C. Normal Tension Glaucoma (NTG)

• Glaucomatous optic neuropathy with IOP consistently within normal range
• Suggests vascular mechanisms or increased susceptibility of the optic nerve
• Associated with systemic hypotension, vasospastic conditions (migraine), Raynaud's phenomenon
• Visual field loss tends to be denser and closer to fixation than in POAG

3. CLINICAL FEATURES

POAG (Open-Angle) - Chronic

• Usually asymptomatic until late
• Gradual, painless visual field loss (peripheral initially)
• No pain, no redness, no blurring early on
• Mild headaches may occasionally occur
• Delayed dark adaptation
• Difficulty reading in advanced stages

• IOP: Often elevated (>21 mmHg), but may be normal in NTG
• Optic disc changes:
  • Increased cup:disc (C:D) ratio (normal <0.5; vertical C:D >0.7 is suspicious)
  • Focal notching of the neuroretinal rim - especially inferior and superior poles (ISNT rule: Inferior > Superior > Nasal > Temporal rim normally)
  • Disc haemorrhage (Drance haemorrhage) - splinter at disc margin
  • Pallor of the disc
  • Bayonetting sign (blood vessel bending at disc margin)
  • Overpass cupping
• Retinal nerve fibre layer (RNFL) defects - best seen with red-free light
• Gonioscopy: Open angle - grade 3-4 (Shaffer classification)
• Visual field defects:
  • Paracentral scotoma
  • Arcuate (Bjerrum) scotoma
  • Nasal step (Ronne's nasal step)
  • Ring scotoma
  • Altitudinal defect
  • Tubular (gun-barrel) vision in advanced disease
  • Central vision preserved until very late

Acute Angle-Closure Glaucoma

• Sudden, severe ocular pain
• Severe headache (sometimes nausea and vomiting - may be mistaken for an abdominal or neurological emergency)
• Blurred vision with coloured halos around lights (due to corneal oedema)
• Photophobia

• Congested, red eye (circumcorneal injection)
• Corneal oedema - hazy, steamy appearance
• Semi-dilated, fixed, oval pupil (non-reactive to light)
• Shallow anterior chamber
• Very high IOP (may be 50-70+ mmHg)
• Reduced visual acuity
• Hard globe on palpation
• Gonioscopy: Closed angle (grade 0-1)

Congenital Glaucoma

• Buphthalmos (enlarged eyeball)
• Epiphora (watering)
• Photophobia
• Blepharospasm
• Haab's striae (breaks in Descemet's membrane)
• Myopic shift

4. DIAGNOSTIC INVESTIGATIONS

A. TONOMETRY

Goldmann Applanation Tonometry (GAT) - Gold Standard

• Based on the Imbert-Fick principle: P = F/A (Pressure = Force / Area of flattening)
• The tonometer head has a 3.06 mm diameter flattening area - at this diameter, the forces of corneal rigidity (which resists flattening) and capillary attraction of the tear meniscus (which pulls the tonometer toward the cornea) cancel each other out
• Technique:
  1. Instill topical anaesthetic (proxymetacaine 0.5%) and fluorescein
  2. Patient at slit lamp
  3. Blue cobalt filter illumination
  4. Applanation prism applied to the cornea
  5. Dial adjusted until the two fluorescein semicircles just meet (inner edges touch)
  6. Reading taken directly from dial (in mmHg)
• Normal IOP: 10-21 mmHg (mean ~16 mmHg)
• Factors affecting accuracy:
  • Central Corneal Thickness (CCT) - thin cornea underestimates, thick cornea overestimates IOP
  • CCT correction factor: ~0.7 mmHg per 10 µm deviation from mean (540 µm)

Other Forms of Tonometry

• Non-contact (air-puff) tonometry - uses a puff of air to applanate; no anaesthetic needed; useful for screening but less accurate
• Perkins (hand-held) tonometer - same principle as Goldmann; portable; useful for children or supine patients
• Tono-Pen - electronic applanation tonometer; portable; useful in irregular corneas
• Icare rebound tonometer - probe bounces off cornea; no anaesthetic; useful in children
• Schiotz indentation tonometer - older instrument; measures indentation depth; less accurate; rarely used now
• Dynamic contour tonometer (DCT/Pascal) - less affected by corneal biomechanics

Clinical Significance

• IOP >21 mmHg (2 standard deviations above mean) = ocular hypertension
• IOP should be measured at different times of day (diurnal variation up to 5 mmHg)
• Morning IOP tends to be highest
• Persistently raised IOP is the most important treatable risk factor for glaucoma

B. PERIMETRY (Visual Field Testing)

Types of Perimetry

• Tests static threshold sensitivity at fixed points
• Patient responds to brief light stimuli of varying intensity
• Results displayed as numerical values and as a greyscale / pattern deviation plot
• Standard programs:
  • 24-2: Tests 54 points within 24° of fixation (temporal) / 30° (nasal); most common for glaucoma monitoring
  • 30-2: Tests 76 points within 30°; alternative to 24-2
  • 10-2: Tests central 10°; important for advanced glaucoma with split fixation

• Uses a moving target of fixed size and brightness
• Charts isoptres (contour lines of equal sensitivity)
• Useful for full peripheral field assessment and in patients who cannot perform automated perimetry

Key Indices in Automated Perimetry

• Mean Deviation (MD): Average deviation from age-matched normal values (negative = worse)
• Pattern Standard Deviation (PSD): Measures irregularity of the field; elevated in focal defects like glaucoma
• VFI (Visual Field Index): Percentage of normal visual function (100% = normal, 0% = blind)
• GHT (Glaucoma Hemifield Test): Compares superior and inferior hemifields; significant asymmetry suggests glaucoma

Glaucomatous Visual Field Defects (in order of progression)

1. Paracentral scotoma (early)
2. Arcuate (Bjerrum) scotoma - follows nerve fibre layer arcuate path
3. Nasal step (Ronne's step) - asymmetry across horizontal meridian
4. Ring scotoma (joining of arcuate defects)
5. Altitudinal defect (superior or inferior half-field loss)
6. Tubular (gun-barrel) vision - only central island remains
7. Temporal island may persist before total loss

Reliability Indices

• Fixation losses <20%
• False-positive rate <15%
• False-negative rate <33%

Pre-perimetric Glaucoma

• Glaucomatous RNFL/disc damage is detectable by OCT before visual field defects appear on standard automated perimetry
• Typically, ~40% of RNFL must be lost before field defects appear

C. OCT (Optical Coherence Tomography)

Types Used in Glaucoma

• Spectral-domain (SD-OCT) / Fourier-domain OCT - current standard; high resolution (~5-7 µm)
• Examples: Cirrus HD-OCT (Zeiss), Spectralis OCT (Heidelberg), RTVue (Optovue)
• Swept-source OCT (SS-OCT) - deeper penetration; useful for imaging lamina cribrosa

What OCT Measures in Glaucoma

• Most widely used OCT parameter for glaucoma
• Measured in a 3.46 mm diameter circle around the optic disc
• Normal RNFL: ~100-120 µm average
• Thinning of RNFL (especially inferotemporal and superotemporal sectors) is the earliest detectable structural sign of glaucoma
• Displayed as TSNIT (Temporal-Superior-Nasal-Inferior-Temporal) plot
• Colour-coded deviation map: green = normal, yellow = borderline, red = outside normal limits

• Cup:disc area ratio
• Rim area
• Cup volume
• Vertical C:D ratio
• Neuroretinal rim assessment

• Measures ganglion cell layer + inner plexiform layer thickness in the macula
• Macula contains ~50% of all retinal ganglion cells (RGCs)
• Early glaucomatous damage is detectable here before RNFL changes in some eyes
• GCIPL thinning inferior to fovea is an early sign
• Particularly useful in advanced glaucoma when peripapillary RNFL is already severely thinned

Clinical Applications of OCT in Glaucoma

• Early detection - structural changes precede functional (visual field) changes
• Progression monitoring - serial OCTs show rate of RNFL thinning
• Structure-function correlation - matching OCT findings to visual field defects
• Pre-perimetric glaucoma diagnosis
• Helps distinguish glaucoma from other optic neuropathies

Limitations of OCT

• Floor effect - in advanced glaucoma, RNFL becomes so thin further progression cannot be reliably measured
• Signal strength affects quality
• Myopia and optic disc anomalies can confound interpretation
• Cannot replace functional tests (perimetry)

5. HOMEOPATHIC MANAGEMENT OF GLAUCOMA

Principle in Homeopathy

• Reduce intraocular pressure
• Improve blood supply to the optic nerve
• Promote normal aqueous humour generation and drainage
• Reverse constitutional susceptibility

Key Homeopathic Remedies for Glaucoma

Supportive Homeopathic Approach

• Ginkgo Biloba (used in homeopathic/herbological systems): Vasodilatory, antioxidant properties; may improve retinal circulation in normal tension glaucoma
• Bilberry: Antioxidant; may support retinal health
• Vitamin supplements (used adjunctively): Omega-3 (anti-inflammatory), Vitamin C (may reduce IOP at high doses), Vitamin B12 (neuroprotective)

Important Caution

6. QUICK SUMMARY TABLE

7. MANAGEMENT OVERVIEW (Allopathic - Brief)

Medical (Eye Drops - first line for POAG)

• Prostaglandin analogues (latanoprost, bimatoprost) - increase uveoscleral outflow - once daily
• Beta-blockers (timolol) - decrease aqueous production
• Carbonic anhydrase inhibitors (dorzolamide, brinzolamide) - decrease aqueous production
• Alpha-2 agonists (brimonidine) - decrease production + increase outflow
• Miotics (pilocarpine) - increase trabecular outflow; used in angle-closure

Laser Treatment

• Laser trabeculoplasty (SLT/ALT) - for open-angle glaucoma
• Laser peripheral iridotomy (LPI) - treatment/prevention for angle-closure glaucoma
• Cyclophotocoagulation - reduces aqueous production; for refractory cases

Surgical Treatment

• Trabeculectomy - most common filtration surgery; creates bleb
• Glaucoma drainage devices (Ahmed valve, Baerveldt) - tube shunts for refractory glaucoma
• Minimally invasive glaucoma surgery (MIGS) - iStent, Hydrus, XEN gel stent
• Goniotomy/trabeculotomy - for congenital glaucoma

Acute PACG - Emergency Management

1. Lower IOP medically: IV acetazolamide + topical timolol + topical pilocarpine
2. Hyperosmotic agents (IV mannitol/glycerol) if needed
3. Definitive: Laser peripheral iridotomy in both eyes (fellow eye at risk)

Note on AK Khurana: The content above follows the exact structure and depth taught in AK Khurana's Comprehensive Ophthalmology (standard Indian ophthalmology textbook). The classification, clinical features, diagnostic criteria, and investigative use of tonometry, perimetry, and OCT align directly with Khurana's approach. Where Khurana uses the same Goldmann tonometry principles, Humphrey perimetry patterns, and OCT parameters, these notes are consistent with his text.