One pupil might be bigger than the other due to a condition called anisocoria, which is when the pupils are of unequal sizes. This can be caused by several factors, including:
- Physiological anisocoria, which is a benign and natural variation present in about 20% of people without underlying health issues.
- Pharmacological causes, such as the effects of certain eye drops, medications, or recreational drugs.
- Pathological conditions such as third nerve palsy (which may cause pupil dilation and drooping eyelid), Horner’s syndrome (characterized by a constricted pupil, drooping eyelid, and decreased sweating), Adie’s tonic pupil (enlarged pupil with poor light response), trauma or injury to the eye or head, brain tumors, strokes, or infections affecting the nervous system pathways controlling the eye.
Slight differences in pupil size are common and can even be genetic or temporary. However, if there is a sudden change in pupil size, if the difference is large, or if it is accompanied by other symptoms such as vision changes, eye pain, drooping eyelids, or headaches, medical evaluation is advised promptly to rule out serious conditions.
