What is Quetiapine (Seroquel)?
Quetiapine is a second-generation (atypical) antipsychotic medication approved for the treatment of schizophrenia and bipolar disorder [1.4.8]. Its therapeutic effects are believed to come from its ability to balance the levels of key neurotransmitters in the brain, primarily dopamine and serotonin [1.4.8]. However, its mechanism of action is complex, as it interacts with a wide range of receptors, including dopamine (D1, D2), serotonin (5-HT1A, 5-HT2A), histamine (H1), and adrenergic (α1, α2) receptors [1.4.1]. This broad receptor profile is responsible for both its therapeutic benefits and its potential side effects.
Understanding Pupil Dynamics: Miosis and Mydriasis
The pupil is the opening in the center of the iris that allows light to enter the eye. Its size is controlled by two opposing muscles:
- Iris Sphincter Muscle: This muscle constricts the pupil (miosis) and is controlled by the parasympathetic nervous system (cholinergic signals).
- Iris Dilator Muscle: This muscle widens the pupil (mydriasis) and is controlled by the sympathetic nervous system (adrenergic signals).
Medications can influence pupil size by interfering with these nerve signals. An anticholinergic drug can cause mydriasis by blocking the constrictor muscle, while an anti-adrenergic (or adrenergic blocker) can cause miosis by inhibiting the dilator muscle [1.3.8, 1.5.1].
The Dual-Action Pharmacology of Quetiapine on the Eye
Quetiapine's potential to affect pupil size is complex because it has properties that could theoretically cause both miosis and mydriasis. The actual effect can depend on the dosage, individual patient physiology, and interaction with other medications.
The Pathway to Miosis: Alpha-1 Adrenergic Blockade
Quetiapine is known to have α1-adrenergic receptor blocking properties [1.4.1]. The iris dilator muscle is activated by alpha-1 adrenergic receptors. By blocking these receptors, quetiapine can prevent the iris dilator muscle from contracting, leading to a relative over-action of the sphincter muscle. This results in pupil constriction, or miosis [1.3.8]. While not a common side effect, several second-generation antipsychotics, including quetiapine, have been linked to miosis through this mechanism [1.2.7, 1.3.8]. Furthermore, at least one case report has documented miosis in a patient following a quetiapine overdose [1.2.4].
The Pathway to Mydriasis: Anticholinergic Effects
Conversely, many antipsychotics, including quetiapine, exhibit anticholinergic properties [1.5.2, 1.5.9]. Anticholinergic drugs block the action of acetylcholine on the iris sphincter muscle. This prevents the pupil from constricting, leading to pupil dilation, or mydriasis [1.4.3, 1.5.1]. This effect is generally considered a more typical, though still infrequent, ocular side effect for this class of drugs compared to miosis [1.3.4]. Blurred vision, another common anticholinergic side effect, is also frequently reported with quetiapine [1.3.1].
Ocular Side Effects Comparison: Antipsychotics
Different antipsychotics have varying affinities for receptors, leading to different side effect profiles. Here is a general comparison based on available data:
| Side Effect | Quetiapine | Olanzapine | Aripiprazole | Chlorpromazine (Typical) |
|---|---|---|---|---|
| Miosis | Possible, via α1-blockade [1.3.8] | Linked [1.3.8] | Linked [1.3.8] | Linked [1.3.8] |
| Mydriasis | Possible, via anticholinergic effect [1.3.4] | High affinity for muscarinic receptors [1.5.2] | Possible | Less common than with other drug classes [1.5.5] |
| Blurred Vision | Common [1.3.1] | Yes | Yes [1.2.6] | Yes |
| Cataracts | Associated; monitoring recommended [1.3.2] | Possible | Cariprazine has a known association [1.2.6] | Common with high, prolonged dosage [1.3.6] |
| Oculogyric Crisis | Rare cases reported [1.5.4] | Highest signal intensity [1.2.6] | High signal for blepharospasm [1.2.6] | More common with high-potency typicals |
Other Significant Eye-Related Side Effects of Quetiapine
Beyond pupil size, quetiapine has been associated with several other ocular side effects that patients should be aware of:
- Blurred Vision and Dry Eyes: These are among the more common ocular effects, often linked to the drug's anticholinergic activity [1.3.1, 1.3.4].
- Cataract Formation: The potential for cataract development has been noted, and some guidelines recommend eye exams at the beginning of treatment and periodically thereafter to monitor for changes in the lens [1.3.2, 1.3.9].
- Increased Intraocular Pressure (IOP): Cases of elevated eye pressure have been reported, which is a concern for patients with or at risk for glaucoma. This may be more likely at higher doses [1.4.1].
- Central Serous Chorioretinopathy (CSCR): This is a rare condition involving fluid accumulation under the retina, which has been documented in case reports linked to quetiapine use [1.2.9, 1.4.6].
- Uncontrolled Eye Movements: Like other antipsychotics, quetiapine can cause uncontrolled muscle movements, which can affect the eyes (e.g., oculogyric crisis, excessive blinking) [1.3.7, 1.5.4].
What to Do for Vision Changes
Patients taking quetiapine should never alter their dose or stop the medication without consulting their doctor. Any new or worsening vision changes—such as blurred vision, eye pain, seeing halos around lights, or noticeable changes in pupil size—should be reported to a healthcare provider promptly for evaluation [1.3.2, 1.3.7].
Conclusion
So, can quetiapine cause miosis? The pharmacological evidence indicates that it is possible, primarily through its alpha-1 adrenergic blocking effects [1.3.8]. However, this is not a common or expected side effect. The drug's competing anticholinergic action makes mydriasis (pupil dilation) and blurred vision more classically associated with its ocular profile [1.4.3]. The key takeaway is that quetiapine possesses a complex and varied impact on the eyes. While serious ocular adverse events are rare, they are possible, highlighting the importance of regular medical supervision and immediate reporting of any visual symptoms.
