A seizure is a sudden, uncontrolled electrical disturbance in the brain that causes changes in behavior, movements, feelings, or consciousness. These neurological events are characterized by abnormal and excessive firing of nerve cells. Observable signs, particularly those involving the eyes, are valuable indicators for witnesses and medical professionals attempting to understand the event. Whether pupils dilate during a seizure is complex, depending heavily on the specific seizure type and the area of the brain where the electrical activity originates. This variability highlights how the eyes provide a direct window into the brain’s chaotic activity during an ictal event.
The Autonomic Nervous System and Pupillary Control
The diameter of the pupil is regulated by the involuntary actions of the Autonomic Nervous System (ANS), which maintains internal body functions outside of conscious control. This system has two primary branches that work in opposition to control the iris muscles responsible for pupil size. The sympathetic nervous system, associated with the “fight or flight” response, triggers pupillary dilation (mydriasis) via the contraction of the radial muscles. Conversely, the parasympathetic nervous system, responsible for “rest and digest” functions, causes pupillary constriction (miosis) when the circular sphincter muscle contracts. The balance of activity between these two branches determines the final pupil size.
Seizures, being intense neurological events, often involve a massive discharge of electrical activity that can significantly disrupt this delicate ANS balance. Depending on which brain regions are involved, the sympathetic or parasympathetic pathways can be overstimulated, leading to rapid and sometimes dramatic changes in pupil size.
Pupillary Response Across Different Seizure Types
Pupillary changes are a common autonomic feature of seizures, but the specific response—dilation or constriction—is not uniform and varies with the seizure’s classification.
In generalized tonic-clonic seizures, which involve widespread electrical activity across both hemispheres of the brain, a strong, bilateral pupillary dilation is the typical finding. This mydriasis is a direct result of the intense sympathetic activation that accompanies the full seizure, similar to other involuntary signs like rapid heart rate and increased blood pressure. During the main part of a tonic-clonic seizure, the pupils may also become nonreactive to light, meaning they will not constrict when illuminated. Following the seizure, during the postictal phase, the pupils typically return to their normal size and reactivity as the brain’s function stabilizes.
Pupillary changes are less predictable in focal seizures, which begin in only one part of the brain. While dilation is still the most common pupillary change, it can sometimes be unilateral or asymmetric, depending on where the seizure originates and how it spreads. Focal seizures affecting the temporal or frontal lobes, which are involved in autonomic control, are more likely to cause pupillary changes. In rare cases involving specific cortical regions, the seizure can cause pupillary constriction (miosis). The presence of any pupillary change during a focal seizure depends on the extent to which the ictal discharge engages the autonomic control centers.
Other Critical Ocular Signs During a Seizure
Beyond simple changes in pupil size, other involuntary eye signs provide valuable information about the seizure’s origin and spread.
One of the most common and clinically relevant is forced eye deviation, known as conjugate gaze deviation, where both eyes turn sharply in one direction. This forced gaze is often directed away from the side of the brain where the seizure activity is starting.
The eyes may also exhibit nystagmus, characterized by rapid, rhythmic, and involuntary movements of the eyeballs. Epileptic nystagmus is a subtle sign seen in seizures originating from the posterior cortical regions, such as the parieto-occipital area. The direction of the fast phase of this eye movement usually beats away from the seizure’s focal point.
A fixed, vacant, or blank stare is characteristic of absence seizures. During this type of generalized seizure, the person stops their activity and stares momentarily into space, often accompanied by a loss of awareness. This fixed gaze can also occur in focal impaired awareness seizures, providing an important observable clue to the type of neurological event taking place.