Understanding Diplopia and Its Causes
Diplopia, commonly known as double vision, is the perception of two images of a single object. It can be monocular (persisting when one eye is closed) or binocular (present only when both eyes are open) [1.3.4]. While many underlying medical conditions can cause diplopia, it is also a known side effect of numerous medications [1.2.4]. This is referred to as drug-induced diplopia. The onset of this condition after starting a new medication or changing a dose should prompt immediate consultation with a healthcare provider.
How Can Medications Cause Double Vision?
Medications can induce diplopia through several mechanisms, disrupting the complex system that controls eye alignment and movement [1.6.1, 1.6.6]. These mechanisms include:
- Central Nervous System (CNS) Disruption: Many drugs act on the brain and can interfere with the neural pathways that control ocular alignment and motility. Anticonvulsants and psychiatric medications are common examples [1.6.2].
- Neuromuscular Blockade: Some drugs can affect the neuromuscular junction where nerves transmit signals to the extraocular muscles, weakening them and causing misalignment [1.6.5].
- Direct Muscle or Nerve Toxicity: Certain medications can be directly toxic to the extraocular muscles or the cranial nerves (III, IV, VI) that control them [1.6.6]. For instance, fluoroquinolone antibiotics are thought to cause tendinitis in the extraocular muscles [1.6.4].
- Impaired Accommodation or Convergence: Drugs can affect the ciliary muscle's ability to focus (accommodation) and converge the eyes for near vision, leading to diplopia [1.6.1].
Common Classes of Medications That Cause Diplopia
A wide range of medications has been associated with diplopia. While it may be a rare side effect for some, for others, it is more common [1.4.1].
Anticonvulsants and Antiepileptics
This class is frequently cited as a cause of diplopia. The risk is often dose-dependent. Antiseizure medications like zonisamide and vigabatrin carry some of the highest risks for drug-induced eye movement disorders [1.4.4].
- Topiramate (Topamax): Used for seizures and migraines, it can cause various visual disturbances, including diplopia [1.2.8, 1.3.2].
- Carbamazepine (Tegretol) and Phenytoin (Dilantin): These older anticonvulsants, especially when used in combination, can impair vergence mechanisms and lead to diplopia [1.6.3].
- Gabapentin (Neurontin) and Pregabalin (Lyrica): Commonly prescribed for nerve pain and seizures, both list diplopia as a potential side effect [1.2.2, 1.2.4].
- Lamotrigine (Lamictal): Diplopia has been reported in about 5.4% of pediatric patients treated with lamotrigine in one clinical database comparison [1.6.8].
Antibiotics
Certain antibiotics can affect vision, with fluoroquinolones being a notable group.
- Fluoroquinolones (e.g., Ciprofloxacin, Moxifloxacin): These are associated with diplopia, possibly due to causing tendinitis of the extraocular muscles [1.6.4]. One study found the median time to onset was 9.6 days after starting therapy [1.3.5].
- Doxycycline: Long-term use of this tetracycline antibiotic can lead to idiopathic intracranial hypertension (IIH), a condition of increased pressure around the brain that can cause diplopia and headaches [1.2.8].
Cardiovascular Drugs
Medications used to treat heart conditions can also be culprits.
- Amiodarone (Cordarone): Used for irregular heartbeats, this drug commonly causes vortex keratopathy, but can also lead to optic nerve damage and diplopia at higher doses [1.2.8, 1.2.7].
- Digoxin (Lanoxin): Can cause a range of vision changes, including blurred vision, altered color perception, and diplopia [1.2.8].
- Beta-blockers and Calcium Channel Blockers: Though rarer, these have been reported to cause diplopia, potentially by affecting neuromuscular transmission [1.6.2].
Psychiatric and CNS Medications
This broad category includes antidepressants, antipsychotics, and sedatives.
- Antidepressants (SSRIs, TCAs): Drugs like sertraline (Zoloft), citalopram (Celexa), and bupropion (Wellbutrin) have been linked to diplopia, though it's considered a rare adverse effect [1.4.1, 1.2.9].
- Antipsychotics: Agents like aripiprazole (Abilify) and risperidone have been associated with eye movement disorders [1.4.4, 1.3.8].
- Benzodiazepines (e.g., Alprazolam, Lorazepam): These can cause diplopia through their CNS-depressant effects [1.2.2, 1.5.8].
Other Notable Medications
- Corticosteroids (e.g., Prednisone): Prolonged use can lead to glaucoma and cataracts, which can cause vision changes including, in some cases, diplopia [1.2.3].
- Botulinum Toxin (Botox): When used for cosmetic or therapeutic reasons near the eyes, the toxin can migrate and inadvertently affect extraocular muscles, causing temporary diplopia [1.6.2, 1.5.2].
Comparison of Common Culprit Medications
| Drug Class | Common Examples | Suspected Mechanism | Frequency/Risk |
|---|---|---|---|
| Anticonvulsants | Topiramate, Gabapentin, Lacosamide, Zonisamide | CNS disruption of ocular alignment; impaired vergence [1.6.3, 1.4.4] | Very Common to Common (e.g., Lacosamide ≥1/10) [1.4.3] |
| Antibiotics | Ciprofloxacin, Moxifloxacin, Doxycycline | Tendinitis of extraocular muscles (Fluoroquinolones); IIH (Doxycycline) [1.6.4, 1.2.8] | Rare (e.g., Ciprofloxacin <1/1000) [1.2.4] |
| Cardiovascular | Amiodarone, Digoxin | Optic nerve damage; direct toxicity [1.2.8, 1.6.2] | Uncommon to Rare |
| Psychiatric | Sertraline, Aripiprazole, Lorazepam | Disruption of ocular motor control via CNS pathways [1.6.2, 1.4.4] | Rare [1.4.1] |
Diagnosis and Management
If you experience double vision, it's crucial to seek medical evaluation. A healthcare provider will take a detailed history, including a list of all medications (prescription and over-the-counter) [1.3.6]. The diagnosis of drug-induced diplopia is often one of exclusion, meaning other potential causes must be ruled out [1.3.2].
Management typically involves:
- Consulting the Prescribing Doctor: Do not stop any medication without medical advice. The first step is always to contact the doctor who prescribed the drug.
- Dechallenge: The doctor may decide to discontinue the suspected medication to see if the diplopia resolves. This is known as a "dechallenge" [1.3.5]. In many cases, symptoms fully resolve upon stopping the drug [1.3.2].
- Dose Adjustment: Sometimes, simply lowering the dose of the medication can alleviate the side effect.
- Supportive Treatment: While waiting for the diplopia to resolve, supportive measures can be used. These include wearing an eye patch on one eye, using prism lenses in glasses to merge the two images, or, in some cases, vision therapy [1.5.1, 1.5.2, 1.5.6].
Conclusion
Diplopia can be a disorienting and concerning side effect of many common medications. It arises from various mechanisms that disrupt the precise coordination of eye movements. Key medication classes implicated include anticonvulsants, certain antibiotics, cardiovascular drugs, and psychiatric medications. Recognizing the link between a new medication and the onset of double vision is critical. Patients should never alter their medication regimen on their own but should immediately report such symptoms to their healthcare provider for proper diagnosis and management, which often leads to complete resolution of the visual disturbance.
Authoritative Link: For more information on double vision, visit the American Academy of Ophthalmology's patient education pages. https://www.aao.org/eye-health/symptoms/double-vision
