Czarnecki et al used a flow diagram to diagnose the cause of unequal pupils (anisocoria). The authors are from the Universities of Toronto, British Columbia and Iowa.
Initial evaluation: Is the inequality of the pupils greater in the dark or the light?
A greater difference in the dark suggests that the dilator muscle of the smaller pupil is weak, associated with a sympathetic lesion.
A greater difference in the light suggests that the sphincter muscle of the larger pupil is weak, associated with a parasympathetic lesion.
Inequality Greater in Light
If the inequality is greater in the light, then the iris is examined using a slit lamp.
If the iris is torn and transilluminates, then the diagnosis is local iris damage. Often there is a history of trauma.
If the iris is intact, then the pupil is evaluated for evidence of Holmes-Adie syndrome with the dilated pupil:
(1) segmental palsy of the sphincter
(2) diminished tendon reflexes
(3) papillary light-near dissociation
The diagnosis is confirmed by hypersensitivity of the dilated pupil to dilute pilocarpine (< 0.125%).
If there is no evidence of Holmes-Adie syndrome, and if the pupil constricts with 1% pilocarpine solution, then the patient has a third nerve palsy.
If there is no evidence of Holmes-Adie syndrome, and if the pupil does not constrict with 1% pilocarpine solution, then the patient has atropinic mydriasis.
Inequality in Dark
If the smaller pupil is slow to dilate, consider Horner’s syndrome. This is confirmed by lesser dilatation of the smaller pupil after installation of 10% cocaine drops.
If the smaller pupil is tonic, consider an old miotic pupil in a patient with Holmes-Adie Syndrome.
If the patient has Horner’s syndrome and 1% hydroxyamphetamine drops dilates both pupils equally, then the patient has central or preganglionic Horner’s syndrome.
If the patient has Horner’s syndrome and the smaller pupil dilates less after 1% hydroxyamphetamine drops, then the patient has postganglionic Horner’s syndrome.
If the smaller pupil is not slow to dilate, then consider simple anisocoria. This is confirmed by equal dilatation of both pupils after installation of 10% cocaine drops.
