What is the difference between open-angle glaucoma and closed-angle glaucoma?

From the Guidelines

The main difference between open-angle and closed-angle glaucoma lies in their mechanism and presentation, with open-angle glaucoma developing gradually due to inefficient fluid drainage and closed-angle glaucoma occurring suddenly when the iris blocks the drainage angle, causing severe symptoms. Open-angle glaucoma, as described in the primary open-angle glaucoma preferred practice pattern 1, is a chronic ocular disease process that is progressive, generally bilateral, but often asymmetric, associated with evidence of optic nerve damage and open anterior chamber angles. In contrast, closed-angle glaucoma, discussed in the primary angle-closure disease preferred practice pattern 1, occurs when the iris blocks the drainage angle, leading to sudden pressure spikes and symptoms such as severe eye pain, headache, nausea, blurred vision, and halos around lights.

Key Differences

• Open-angle glaucoma:
  • Gradual development
  • No symptoms until vision loss occurs
  • Managed with daily eye drops, oral medications, laser therapy, or surgery
• Closed-angle glaucoma:
  • Sudden onset
  • Severe symptoms
  • Requires immediate intervention with medications and laser peripheral iridotomy

Treatment Approaches

The treatment approaches for open-angle and closed-angle glaucoma differ significantly. Open-angle glaucoma is managed with daily eye drops (like latanoprost, timolol, or brimonidine), oral medications, laser therapy (trabeculoplasty), or surgery to improve drainage 1. In contrast, closed-angle glaucoma requires immediate intervention with medications to rapidly lower pressure (IV acetazolamide, topical beta-blockers, alpha-agonists), followed by laser peripheral iridotomy to create a small hole in the iris to restore proper fluid flow 1.

Importance of Early Detection

Regular eye exams are crucial for detecting open-angle glaucoma, as it typically has no symptoms until vision loss occurs 1. Closed-angle glaucoma, on the other hand, presents as an emergency with severe symptoms, requiring immediate medical attention 1. The anatomical difference between the two types of glaucoma explains why closed-angle glaucoma can cause sudden, painful attacks while open-angle glaucoma silently damages vision over years without noticeable symptoms.

From the FDA Drug Label

For adjunctive treatment of: ... chronic simple (open-angle) glaucoma, secondary glaucoma, and preoperatively in acute angle-closure glaucoma ... The dosage employed in the treatment of chronic simple (open-angle) glaucoma ranges from 250 mg to 1 g of acetazolamide per 24 hours, usually in divided doses for amounts over 250 mg. In treatment of secondary glaucoma and in the preoperative treatment of some cases of acute congestive (closed-angle) glaucoma, the preferred dosage is 250 mg every four hours, although some cases have responded to 250 mg twice daily on short-term therapy

The main difference between open and closed angle glaucoma is the treatment approach and dosage of acetazolamide.

• Open-angle glaucoma: treated with 250 mg to 1 g of acetazolamide per 24 hours, usually in divided doses.
• Closed-angle glaucoma: treated with 250 mg every four hours, or 250 mg twice daily on short-term therapy, and may require more urgent treatment, such as intravenous therapy, for rapid relief of ocular tension 2 2.

From the Research

Difference between Open and Closed Angle Glaucoma

• Open-angle glaucoma is characterized by an increase in intraocular pressure due to impaired drainage of aqueous humor, while closed-angle glaucoma is caused by a blockage of the drainage angle, leading to a sudden increase in intraocular pressure 3.
• The pathophysiological mechanisms underlying open-angle and closed-angle glaucoma are distinct, with open-angle glaucoma involving a slow clogging of the drainage canals, and closed-angle glaucoma involving a sudden blockage of the drainage angle 3.
• Latanoprost, a prostaglandin F2-alpha analogue, has been shown to be effective in reducing intraocular pressure in patients with open-angle glaucoma or ocular hypertension, with a single daily dose regimen and minimal systemic adverse effects 4, 5, 6, 7.
• In contrast, the use of latanoprost in closed-angle glaucoma is less well-studied, although some evidence suggests that it may be effective in reducing intraocular pressure in patients with elevated IOP after undergoing iridotomy 4.
• The morphology of the optic disc and surrounding tissues, genetic characteristics, and optical coherence tomography angiography may contribute to a deeper comprehension of the underlying pathogenesis of glaucoma and enhance the management of different types of this ocular condition 3.

Treatment Options

• Latanoprost has been shown to be a valuable addition to first-line treatment alternatives for glaucoma, ocular hypertension, and even angle-closure glaucoma, due to its efficacy, convenient administration schedule, and minimal systemic adverse effects 4, 5, 6, 7.
• The fixed combination of latanoprost plus timolol has been shown to be significantly more effective than either of its individual components in reducing intraocular pressure 4.
• Latanoprost has also been shown to have a good safety and tolerability profile, with minimal ocular adverse events, such as conjunctival hyperaemia and iris colour change, which are generally mild and transient 4, 5, 6.