SNRIs and Open Angle Glaucoma
SNRIs can be used in patients with open angle glaucoma, but require rigorous ophthalmologic monitoring with regular IOP checks, as these medications pose a risk primarily for angle-closure glaucoma rather than worsening open angle disease. 1, 2
Key Distinction: Open Angle vs. Angle-Closure Risk
The primary concern with SNRIs is precipitating acute angle-closure glaucoma in susceptible individuals, not worsening pre-existing open angle glaucoma. 3 The FDA label for duloxetine explicitly states that "pre-existing glaucoma is almost always open-angle glaucoma" and that "open-angle glaucoma is not a risk factor for angle-closure glaucoma." 3 This is a critical distinction that is often misunderstood in clinical practice.
Mechanism of SNRI-Related Ocular Effects
SNRIs can cause:
- Mild pupillary dilation (mydriasis) through adrenergic effects, which can precipitate angle-closure in anatomically susceptible patients 3, 4
- Ciliary body effusion leading to anterior chamber shallowing 5
- Potential weak anticholinergic activity despite being marketed as lacking significant muscarinic receptor binding 6, 4
Clinical Management Algorithm
Before Initiating SNRI Therapy:
- Obtain baseline ophthalmologic examination documenting optic nerve status, visual field, and IOP 1
- Assess anterior chamber depth and iridocorneal angle configuration to identify patients at risk for angle-closure (not a concern for established open angle glaucoma patients) 3
- Document baseline IOP measurements to establish target pressure (approximately 20% below baseline) 1, 7
During SNRI Treatment:
- Maintain rigorous ophthalmologic supervision with regular IOP monitoring 1, 2
- Monitor for symptoms of angle-closure including eye pain, blurred vision, halos around lights, headache, and nausea 1, 5
- For severe or unstable glaucoma, coordinate care between psychiatry and ophthalmology before and during treatment 1
If IOP Elevation Occurs:
- Discontinue the SNRI immediately if acute IOP elevation develops 5, 6, 8
- IOP typically normalizes within 48 hours to 1 week after drug discontinuation 6, 8
- Consider prophylactic laser iridotomy if angle-closure mechanism is suspected 5, 4
Evidence from Case Reports
Multiple case reports document SNRI-related glaucoma events:
- Duloxetine caused bilateral acute angle-closure with IOPs of 52-55 mmHg, resolving after drug discontinuation and laser iridotomy 5
- Venlafaxine increased IOP from 17-18 mmHg to 22-23 mmHg in narrow angle glaucoma patients within 4-16 days, normalizing one week after cessation 6
- Rechallenge with paroxetine (an SSRI with similar mechanism) reproduced IOP elevation from 10 mmHg to 41 mmHg, confirming causality 8
Important Clinical Pitfalls
Do not assume SNRIs are contraindicated in open angle glaucoma—the risk profile differs substantially from angle-closure susceptibility. 3 Patients with established open angle glaucoma who have undergone iridotomy or have wide open angles are at minimal risk for SNRI-induced complications.
Monitor IOP even in asymptomatic patients, as progressive or sub-acute angle-closure may present without dramatic symptoms and could be missed. 9
Educate patients to report visual symptoms immediately, including blurred vision, eye pain, or halos around lights, as these may indicate acute IOP elevation requiring urgent intervention. 3
Ensure medication adherence to glaucoma therapy is maintained, as this is crucial for treatment success and may be affected by depression or pain syndromes being treated with SNRIs. 2