What is Gabapentin?
Gabapentin is an anticonvulsant medication that is also a structural analogue of the neurotransmitter gamma-aminobutyric acid (GABA) [1.5.3, 1.5.5]. Though it was designed to mimic GABA, its primary mechanism of action does not involve binding to GABA receptors [1.5.1, 1.5.8]. Instead, it binds with high affinity to the α2δ-1 subunit of voltage-gated calcium channels [1.5.1, 1.5.6]. This action inhibits the release of excitatory neurotransmitters, which is how it helps control seizures and manage neuropathic pain [1.5.1].
It is commonly prescribed for:
- Epilepsy and partial seizures [1.5.8]
- Neuropathic pain, including postherpetic neuralgia (pain from shingles) and pain from diabetic neuropathy [1.5.8]
- Off-label for various conditions like fibromyalgia and restless legs syndrome [1.3.3, 1.5.1]
Gabapentin is generally considered safe but is associated with side effects like drowsiness, dizziness, and various vision changes [1.3.1, 1.3.4].
The Link Between Gabapentin and Increased Eye Pressure
Recent studies have brought attention to a potential link between gabapentin use and an increase in intraocular pressure (IOP), which is a significant risk factor for glaucoma.
Acute Angle-Closure Glaucoma (AAG)
Acute angle-closure glaucoma is a medical emergency that occurs when the drainage angle in the eye, where the iris meets the cornea, becomes blocked. This blockage prevents aqueous humor (the fluid inside the eye) from draining properly, causing a rapid and painful spike in eye pressure.
Several studies have identified an association between gabapentin and AAG. One large epidemiological study found that gabapentin use within the year prior to diagnosis was associated with a 42% increased risk of developing AAG [1.2.1]. The researchers hypothesized that the mechanism might be similar to that of the drug topiramate, involving a forward displacement of the ciliary body, which narrows the drainage angle [1.2.1, 1.2.2]. While case reports had previously noted this connection, this large-scale study provided more substantial evidence [1.6.4]. Interestingly, the study found the association with use in the year prior to diagnosis, but not necessarily with current use, a finding that researchers noted as odd and requiring further investigation [1.6.3].
Primary Open-Angle Glaucoma (POAG)
Primary open-angle glaucoma is the most common form of glaucoma. It is a chronic condition that progresses slowly as the eye's drainage canals become less efficient over time, leading to a gradual increase in IOP and damage to the optic nerve. A recent large-scale retrospective cohort study using de-identified electronic health records found that both gabapentin and its relative, pregabalin, were associated with an increased risk of developing POAG [1.2.5]. The study, which followed patients for up to five years, showed that gabapentin users had a significantly elevated risk for POAG, overall glaucoma, and ocular hypertension compared to a control group [1.2.5].
Other Vision-Related Side Effects of Gabapentin
Beyond the risk of glaucoma, gabapentin is linked to several other vision side effects. Patients often report these issues, and they are listed as common side effects in drug information leaflets. These include:
- Blurred or Double Vision (Diplopia): This is a frequently reported side effect [1.3.1, 1.3.4]. In clinical trials, double vision was reported in as many as 8% of people taking gabapentin for nerve pain [1.3.3].
- Uncontrolled Eye Movements (Nystagmus): Continuous, rolling, or back-and-forth eye movements are a known side effect [1.3.3, 1.3.8].
- Visual Field Constriction: At least one case report documented a reversible constriction of the visual field in a patient taking gabapentin. The patient's visual field improved and eventually returned to normal after the medication was stopped [1.3.5, 1.3.9].
Comparison of Medications Affecting Eye Pressure
Gabapentin is not the only medication that can affect intraocular pressure. Many common drugs can pose a risk, especially for individuals predisposed to glaucoma.
| Medication Class | Examples | Mechanism of IOP Increase |
|---|---|---|
| Gabapentinoids | Gabapentin | Associated with increased risk of both open-angle and angle-closure glaucoma; may involve ciliary body displacement [1.2.1, 1.2.5]. |
| Corticosteroids | Prednisone, Cortisone sprays | Can increase IOP by clogging the eye's drainage tissue (trabecular meshwork), particularly risky for open-angle glaucoma [1.4.4, 1.4.5]. |
| Anticholinergics | Oxybutynin (Ditropan), Ipratropium (Atrovent) | Cause the pupil to dilate (mydriasis), which can narrow the drainage angle and trigger acute angle-closure glaucoma [1.4.1, 1.4.9]. |
| Antidepressants (SSRIs & Tricyclics) | Fluoxetine (Prozac), Amitriptyline (Elavil) | Can have anticholinergic effects, leading to pupil dilation and risk of angle-closure [1.4.1, 1.4.4]. |
| Sulfa-containing Drugs | Topiramate (Topamax), Acetazolamide | Can cause swelling in ocular structures (uveal effusions), leading to a forward shift of the lens and iris, which can precipitate acute angle-closure glaucoma [1.4.1, 1.4.4]. |
| Antihistamines/Decongestants | Diphenhydramine (Benadryl), Pseudoephedrine | Can have dilating effects on the pupil, which may increase risk in patients with narrow angles [1.4.1, 1.4.8]. |
Conclusion
The evidence increasingly suggests a concerning link between gabapentin use and the risk of developing both acute angle-closure and primary open-angle glaucoma [1.2.1, 1.2.5]. While the drug is effective for managing neuropathic pain and seizures for millions, this potential side effect warrants caution and awareness. Patients with a history of glaucoma, narrow drainage angles, or other risk factors should discuss the use of gabapentin with both their prescribing physician and their ophthalmologist. Any new or worsening eye symptoms—such as eye pain, blurred vision, or seeing halos around lights—while taking gabapentin should be reported to a healthcare provider immediately. Further research is needed to fully understand the causal relationship and the precise mechanisms involved [1.6.1].
Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare professional before making any decisions about your health or treatment.
Visit the American Academy of Ophthalmology for more information on glaucoma.
