Anisocoria is a condition involving an unequal size of the eyes’ pupils, defined by a difference of 0.4mm or more between the sizes of the pupils of the eyes. It affects 20% of the population. It can be an entirely harmless condition, or a Sx of more serious medical problems.

• Physiological anisocoria, which is found in 20% of normal people, who have silght difference in pupil size. The difference however, is usually less than 1mm
• Horner’s syndrome
• Mechanical anisocoria, due to previous trauma, eye surgery, or inflammation (uveitis, angle closure glaucoma), can lead to adhesions between the iris and the lens
• Adie tonic pupil, usually an isolated benign entity, presenting in young women. It may be associated with loss of deep tendon reflex (Adie’s syndrome). It involves delayed dilation of the iris, especially after near stimulus, segmental iris constriction, and sensitivity of pupil to a weak solution of pilocarpine
• Oculomotor nerve palsy, which can be caused by ischemia, intracranial aneurysm, head trauma, and brain tumors. In ischemic lesions of the oculomotor nerve, pupillary function is usually spared whereas in compressive lesions the pupil is involved
• Pharmacological agents, if instilled in 1 eye. Examples of drugs which may affect the pupils include pilocarpine, cocaine, tropicamide, MDMA, dextromethorphan, and ergolines