Anisocoria - Causes and Symptoms

Definition

Anisocoria consists of the difference in size between the two pupils. This phenomenon is physiological in about 20% of healthy people, in which - in terms of size - it causes a difference (in the diameter of the two pupils) of less than a millimeter (NB: in order to speak of anisocoria this difference must be equal or greater at 0.4mm).

Among the pathological causes of anisocoria are iris and neurological dysfunctions. For example, a different pupillary diameter between the two eyes may be due to paralysis of the third cranial nerve (following aneurysm or brain tumor), syphilis and Horner syndrome. Anisocoria may also occur in subarachnoid hemorrhage, in meningitis, in encephalitis, in epilepsy and in some intoxications (eg alcoholism). Furthermore, anisocoria can represent the outcome of a cranial or ocular trauma, dysfunctions in pupil constriction (eg Adie's syndrome) or congenital iris defects. Sometimes, the anisocoria is drug-induced (eg scopolamine and eye drops based on pilocarpine or tropicamide).