Glaucoma is an optic neuropathy that can lead to irreversible vision loss, often associated with elevated intraocular pressure (IOP). While genetics and age are significant risk factors, various medications can also cause or exacerbate the condition. This phenomenon, known as drug-induced glaucoma, occurs through different mechanisms, depending on the drug and the individual's ocular anatomy.
Medications and Open-Angle Glaucoma
Open-angle glaucoma is the most common form, typically developing gradually and with few symptoms in its early stages. The primary mechanism for drug-induced open-angle glaucoma is a medication's effect on the trabecular meshwork, the eye's drainage system. The most well-documented culprits are corticosteroids.
Corticosteroids
Systemic and topical corticosteroids are widely prescribed for various inflammatory and autoimmune conditions, but they are notorious for their potential to increase IOP. The mechanism involves increasing the resistance to aqueous humor outflow at the trabecular meshwork. The risk depends on the potency, dose, and duration of steroid use. Steroid-induced ocular hypertension can occur with various routes of administration, including:
- Topical eye drops: The most frequent cause, with potent formulations like dexamethasone and prednisolone carrying a higher risk.
- Periocular and intravitreal injections: Used to treat eye-related inflammation, these can lead to a significant and prolonged rise in IOP.
- Oral steroids: Long-term use of oral steroids, such as prednisone, is associated with a greater risk of glaucoma and cataracts.
- Inhaled and nasal steroids: Used for asthma and allergies, respectively. High-dose, long-term use has been linked to increased risk, especially in the elderly.
Medications and Angle-Closure Glaucoma
Angle-closure glaucoma (ACG) is a more acute condition where the eye's drainage angle is suddenly blocked, causing a rapid and severe rise in IOP. This can cause headaches, eye pain, and blurred vision, and is considered an ophthalmic emergency. Medication-induced ACG is more likely to occur in individuals with a pre-existing narrow angle or other anatomical predispositions.
Anticholinergics and Sympathomimetics
Many medications have anticholinergic (parasympatholytic) or sympathomimetic (adrenergic) properties, which can cause pupillary dilation (mydriasis). This can trigger a 'pupillary block,' where the iris blocks the eye's drainage angle, causing pressure to build up. Culprits include:
- Respiratory medications: Anticholinergic inhalers like ipratropium and tiotropium for asthma and COPD.
- Cold and flu remedies: Over-the-counter decongestants and antihistamines containing pseudoephedrine or phenylephrine.
- Urinary incontinence medications: Drugs like oxybutynin and tolterodine.
- Psychiatric medications: Older tricyclic antidepressants and some antipsychotics.
- Gastrointestinal medications: Antispasmodics and motion sickness drugs like scopolamine.
Sulfa-Containing Drugs
This class of drugs can cause an idiosyncratic reaction leading to swelling of the ciliary body and a forward displacement of the lens-iris diaphragm, blocking the drainage angle. This mechanism is different from pupillary block and can occur even in eyes with wide angles.
- Topiramate (Topamax): A key example, used for migraines and seizures. Topiramate-induced ACG is typically bilateral and presents acutely within the first few weeks of treatment, often accompanied by a significant myopic shift (nearsightedness).
- Other sulfa drugs: Includes certain antibiotics (e.g., sulfamethoxazole) and diuretics (e.g., hydrochlorothiazide).
Other Medications
Several other drug classes have been linked to increased glaucoma risk:
- Phosphodiesterase type 5 (PDE5) inhibitors: Medications for erectile dysfunction like sildenafil (Viagra) and tadalafil (Cialis). Some studies suggest a potential link to elevated IOP, possibly by increasing blood flow to the ciliary body.
- Tamsulosin (Flomax): Used for benign prostatic hyperplasia (BPH). While not causing glaucoma directly, it is known to cause Intraoperative Floppy Iris Syndrome (IFIS) during cataract or glaucoma surgery, complicating the procedure.
- Anticoagulants: In rare cases, these can lead to spontaneous suprachoroidal hemorrhage, displacing the lens-iris diaphragm forward and causing angle closure.
Comparison Table: Drug-Induced Glaucoma Mechanisms
| Feature | Open-Angle Mechanism | Angle-Closure (Pupillary Block) | Angle-Closure (Non-Pupillary Block) |
|---|---|---|---|
| Primary Drug Class | Corticosteroids (topical, oral, inhaled) | Anticholinergics, sympathomimetics, tricyclic antidepressants | Sulfa-containing drugs (e.g., Topiramate) |
| Underlying Pathophysiology | Increased resistance to aqueous outflow at the trabecular meshwork. | Pupillary dilation causes the iris to block the trabecular meshwork. | Ciliochoroidal effusion or anterior rotation of the ciliary body displaces the iris-lens diaphragm. |
| Onset | Gradual, often over weeks or months. | Rapid, often within hours of taking the medication. | Rapid, usually within the first two weeks of treatment. |
| Effect on Pupil | No direct effect on pupil size. | Causes pupillary dilation (mydriasis). | Mydriasis may or may not be present. |
| Typical Presentation | Asymptomatic until significant optic nerve damage occurs. | Severe eye pain, headache, blurred vision, and halos. | Blurred vision (myopic shift), eye pain, and headache. |
| Patient Risk Factors | Pre-existing glaucoma, family history, high myopia, diabetes. | Narrow anterior chamber angles. | Idiosyncratic reaction, can occur even in eyes with wide angles. |
The Importance of Physician Communication
Managing medication-related glaucoma risk requires close collaboration between patients and healthcare providers. It is crucial to inform all doctors, including ophthalmologists, about your complete medication list, including over-the-counter drugs, herbal supplements, and injections.
If you have a history of glaucoma or have been identified with narrow drainage angles, this information is critical for any physician prescribing new medication. A comprehensive eye exam, including an evaluation of the anterior chamber, is the best way to assess risk.
Conclusion
Many medications, from commonly used steroids to specific antidepressants and decongestants, carry a risk of inducing or worsening glaucoma. While steroid-induced glaucoma typically follows an open-angle mechanism, numerous other systemic drugs can trigger acute angle-closure glaucoma, particularly in susceptible individuals. The key to prevention is awareness, open communication with your healthcare team, and regular eye monitoring, especially when starting a new medication. For example, the American Academy of Ophthalmology offers valuable resources detailing medication-induced angle-closure glaucoma and other ocular adverse effects. Understanding the specific mechanism by which a drug affects eye pressure is vital for correct diagnosis and management, protecting vision from potential harm.
