Physiologic Anisocoria

What is it?

Non-pathologic difference in pupil size between the two eyes (“anisocoria”) in dim illumination
Both pupils constrict normally to light
Topical apraclonidine or cocaine tests are negative

In dim illumination, the pupil size difference between the eyes is no greater than 1.5mm
Pupils constrict normally to bright light
No dilation lag in the smaller pupil when the room light is turned off
After topical instillation of 0.5% apraclonidine into both eyes, there is no change in the size of the pupils
After topical instillation of 10% cocaine, the residual difference in pupil size between the eyes is no greater than 1mm
No other pertinent neuro-ophthalmic findings

Rule out exposure to instilled or aerosolized anticholinergic or sympathomimetic mydriatic agents
Rule out episodic mydriasis by obtaining a history of similar previous short-lived episodes
Perform slit lamp examination to rule out evidence of mild inflammatory, dysplastic, or traumatic iridoplegia
Instill 0.5% apraclonidine in each eye to rule out Horner syndrome, except…
Trap: do not instill apraclonidine into the eyes of children aged 2 years or less because it may provoke life-threatening cardiopulmonary autonomic effects, therefore…
Instill cocaine 10% in children aged 2 years or less to rule out Horner syndrome

Normal constriction to light of both pupils excludes lesions of the preganglionic third nerve, ciliary ganglion and ciliary nerves, pharmacologic blockage, and iris damage
Negative topical pharmacologic diagnostic tests exclude Horner syndrome
Iridoplegia should be evident on slit lamp examination
Physiologic anisocoria may be intermittent and the large pupil may change from one eye to the other
Episodic mydriasis causes a greater difference in pupil size between the eyes than does physiologic anisocoria