What are the types of glaucoma?

Types of Glaucoma

Glaucoma is a heterogeneous group of eye disorders characterized by progressive optic neuropathy with characteristic optic nerve damage and visual field loss that can lead to irreversible blindness if untreated. 1 The main types of glaucoma can be classified based on the anatomy of the anterior chamber angle and underlying etiology.

Primary Open-Angle Glaucoma (POAG)

POAG is the most common form of glaucoma, accounting for approximately 90% of glaucoma cases in North America 2. It is characterized by:

• Open anterior chamber angles on gonioscopy
• Progressive optic nerve damage with characteristic cupping
• Retinal nerve fiber layer (RNFL) thinning
• Visual field defects that correlate with structural damage
• Usually bilateral but often asymmetric progression
• Adult onset (typically)
• Absence of secondary causes 3

POAG severity can be classified as:

• Mild: Optic disc/RNFL abnormalities with normal visual fields
• Moderate: Optic disc/RNFL abnormalities with visual field defects in one hemifield not within 5° of fixation
• Severe: Optic disc/RNFL abnormalities with visual field defects in both hemifields and/or loss within 5° of fixation
• Indeterminate: Optic disc/RNFL abnormalities with unreliable or unavailable visual field testing 3

Normal-Tension Glaucoma (NTG)

• Subset of POAG where IOP remains within normal range (<21 mmHg)
• Nearly 40% of POAG patients have normal IOP measurements 3
• Same characteristic optic nerve damage and visual field loss

Primary Angle-Closure Glaucoma (PACG)

PACG is characterized by:

• Closure of the anterior chamber angle
• Can present acutely (an ophthalmologic emergency) or chronically
• More common in East Asian populations and hyperopic patients 4
• Acute angle-closure attacks present with:
  • Sudden severe eye pain
  • Blurred vision
  • Headache
  • Nausea/vomiting
  • Red eye
  • Mid-dilated, non-reactive pupil 5

Secondary Glaucomas

These develop as a result of other ocular or systemic conditions:

1. Pseudoexfoliation Glaucoma:

   • Associated with deposition of whitish material on anterior segment structures
   • More aggressive course than POAG 3

2. Pigmentary Glaucoma:

   • Caused by pigment dispersion from the iris
   • More common in young myopic males 3

3. Neovascular Glaucoma:

   • Results from abnormal blood vessel growth on the iris and angle
   • Often secondary to retinal ischemia (diabetic retinopathy, central retinal vein occlusion) 3

4. Traumatic Glaucoma:

   • Following blunt or penetrating ocular trauma 3

5. Steroid-Induced Glaucoma:

   • Due to prolonged corticosteroid use (topical, intravitreal, or systemic) 3

6. Uveitic Glaucoma:

   • Secondary to intraocular inflammation 3

Congenital/Developmental Glaucoma

• Present at birth or developing in early childhood
• Often due to abnormal development of the drainage structures
• May be isolated or associated with other ocular or systemic abnormalities 3

Ocular Hypertension

• Elevated IOP (>21 mmHg) without detectable optic nerve damage or visual field loss
• Considered a risk factor for developing POAG rather than a type of glaucoma 3, 5

Clinical Features Common to Most Glaucoma Types

• Optic nerve cupping with increased cup-to-disc ratio
• Violation of the ISNT rule (Inferior rim > Superior rim > Nasal rim > Temporal rim)
• Retinal nerve fiber layer defects
• Characteristic visual field defects (nasal step, arcuate scotoma, paracentral scotoma)
• Optic disc hemorrhages (splinter hemorrhages at the disc margin)
• Beta-zone parapapillary atrophy 3, 1

Understanding the specific type of glaucoma is crucial for determining appropriate treatment strategies, as management approaches differ significantly between open-angle and angle-closure glaucoma 6, 5.