Open-Angle Glaucoma

👁️‍🗨️ Open-Angle Glaucoma (OAG)

Also known as Primary Open-Angle Glaucoma (POAG) — the most common type of glaucoma worldwide.

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🧠 Definition

Open-angle glaucoma is a chronic, progressive optic neuropathy caused by increased resistance to aqueous outflow through the trabecular meshwork, leading to elevated intraocular pressure (IOP) and gradual damage to the optic nerve — even though the anterior chamber angle remains anatomically open.

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🔬 Pathophysiology

• Aqueous humor flows from the ciliary body → posterior chamber → pupil → anterior chamber → drains via trabecular meshwork → Schlemm’s canal → episcleral veins.

• In OAG:

  • The drainage system becomes inefficient over time.

  • Intraocular pressure rises, damaging the retinal ganglion cells and optic nerve fibers, particularly in the superior and inferior poles, leading to cupping and visual field loss.

• Despite the name, the angle remains open on gonioscopy.

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📊 Epidemiology

• Most common in individuals >40 years

• Leading cause of irreversible blindness worldwide

• More prevalent in:

  • African descent

  • Family history of glaucoma

  • Diabetics

  • Myopes (nearsighted)

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🔍 Clinical Features

🐢 Silent Progression (Until late stages)

Early signs	Late signs
Usually asymptomatic	Peripheral vision loss (tunnel vision)
Slight eye discomfort (rare)	Poor night vision
No redness or pain	Eventual central vision loss

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🩺 Diagnosis

1. Tonometry

   • Measures IOP (usually >21 mmHg in POAG)

   • Note: Some POAG patients may have normal IOP (Normal-Tension Glaucoma)

2. Gonioscopy

   • Confirms open angle in anterior chamber

3. Ophthalmoscopy / Fundus Examination

   • Increased cup-to-disc ratio (>0.6)

   • Thinning of neuroretinal rim

   • Optic disc cupping

4. Visual Field Testing (Perimetry)

   • Detects peripheral field defects early

   • Arcuate scotomas, nasal step, paracentral defects

5. OCT (Optical Coherence Tomography)

   • Measures retinal nerve fiber layer thickness and ganglion cell layer loss

6. Pachymetry

   • Measures central corneal thickness (affects accuracy of IOP readings)

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💊 Treatment

🎯 Goal: Lower IOP to prevent progression

1. Medical Therapy (First-line)

Drug Class	Examples	Action
Prostaglandin analogs	Latanoprost, Travoprost	↑ Uveoscleral outflow
Beta-blockers	Timolol, Betaxolol	↓ Aqueous production
Alpha-agonists	Brimonidine	↓ Production & ↑ Outflow
Carbonic anhydrase inhibitors	Dorzolamide, Acetazolamide	↓ Production
Rho kinase inhibitors	Netarsudil	↑ Trabecular outflow

2. Laser Therapy

• Laser Trabeculoplasty

  • Argon (ALT) or Selective (SLT)

  • Enhances trabecular outflow

  • Can be primary or adjunct therapy

3. Surgical Therapy

• Trabeculectomy – Creates alternative drainage route

• Drainage implants (e.g., Ahmed valve)

• Minimally Invasive Glaucoma Surgeries (MIGS) – Safer, for mild/moderate cases

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🔁 Follow-Up

• Lifelong monitoring of:

  • IOP

  • Optic nerve status

  • Visual fields

  • Adherence to medication

• Regular visits every 3–6 months

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⚠️ Complications

• Irreversible blindness if untreated

• Depression and reduced quality of life due to vision loss

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📌 Quick Facts

Feature	Open-Angle Glaucoma
Angle status	Open
Onset	Insidious, chronic
Symptoms	None early; tunnel vision late
Pain/redness	Absent
IOP	Often elevated (>21 mmHg)
Emergency	No

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🧠 Normal-Tension Glaucoma (NTG)

• A subtype of OAG with normal IOP (<21 mmHg)

• Likely due to vascular dysregulation or optic nerve susceptibility

• Risk factors: Low BP, sleep apnea, migraine

• Managed similarly — goal is to lower IOP even further