Pupil dilation, medically known as mydriasis, occurs when the black center of the eye becomes larger than its usual size. The pupil functions as an opening in the iris, the colored part of your eye, controlling the amount of light that enters. Tiny muscles within the iris adjust the pupil’s size, allowing it to expand in dim conditions to let in more light or contract in bright light to limit light exposure.
Why Pupils Dilate
Beyond light, physiological responses also trigger dilation, such as strong emotions like excitement, fear, or arousal, which activate the sympathetic nervous system. This “fight-or-flight” response can cause temporary pupil enlargement.
Dilation can also be medically induced, commonly during eye examinations where special eye drops, called mydriatics, are used to enlarge the pupils. This allows eye care professionals a clearer view of the internal structures of the eye, like the retina and optic nerve. Certain medications, including antihistamines, decongestants, antidepressants, and antispasmodics, can lead to pupil dilation as a side effect. Additionally, recreational substances such as stimulants, hallucinogens, and even alcohol can cause pupils to dilate by affecting neurotransmitter activity in the brain. Head trauma, stroke, or other neurological conditions can also result in pupil dilation.
How Long Dilation Lasts
The duration of pupil dilation varies significantly depending on its cause. Natural dilation due to changes in light or emotional states is typically temporary, lasting only seconds to a few minutes as conditions or feelings shift. This rapid adjustment is a normal physiological function of the eye.
When dilation is induced by eye drops for an eye exam, the duration depends on the specific type of drop used. Tropicamide, a common dilating agent, generally causes dilation for approximately 4 to 6 hours, though some individuals may experience effects for up to 8 hours. Stronger drops, like cyclopentolate, can keep pupils dilated for up to 24 hours, while atropine, used in some cases, can prolong dilation for 7 to 10 days.
Dilation caused by medications or recreational substances is highly variable, ranging from a few hours to several days, depending on the substance, dosage, and an individual’s metabolism. For instance, effects from LSD can last 6 to 18 hours, while psilocybin and mescaline can last 8 to 12 hours. Dilation resulting from underlying medical conditions or injuries, such as brain trauma or certain neurological disorders, can be persistent and may only resolve with treatment of the underlying issue.
When to Consult a Doctor
Consult a doctor if you experience pupil dilation under specific circumstances. If you experience sudden onset of dilation in one or both eyes without an obvious reason, such as changes in light or recent eye drops, it warrants evaluation. Unequal pupil size, known as anisocoria, that is new or worsening should also prompt a medical consultation.
Dilation accompanied by other symptoms like a severe headache, vision changes (such as blurriness or double vision), eye pain, dizziness, nausea, or confusion, indicates a need for immediate medical advice. Dilation that occurs following any head injury or trauma also requires prompt assessment. Similarly, if dilation persists longer than expected for known causes, such as after an eye exam, contacting a healthcare provider is recommended.