Clinical autonomic research : official journal of the Clinical Autonomic Research Society
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Used in the diagnosis of Horner's syndrome, apraclonidine 1% dilatates the involved eye due to denervation supersensitivity. Recent literature suggests that in healthy volunteers, apraclonidine provokes a mild miotic effect. Since the comparison of both the pathologic and the non-pathologic eye is important, we wanted to further investigate the effect of apraclonidine on the healthy eye. By measuring the effect on the pupil intermittently over a few hours, we tried to determine the best moment for evaluation after instillation with apraclonidine. Therefore, the effect of apraclonidine on pupillary parameters was investigated in 14 healthy volunteers. ⋯ Instillation of apraclonidine 1% in healthy subjects causes relative miosis, which is most pronounced after 30-60 min. The amplitude of constriction to light also differs significantly. The relative miotic effect of apraclonidine could be explained by the α-2 receptor agonistic effect which is more pronounced than the α-1 agonistic effect in healthy subjects. In patients with Horner's syndrome, the α-1 agonistic effect will dominate because of the supersensitivity of the α-1 receptors, resulting in relative mydriasis. These findings stress the necessity to instill the unaffected eye in diagnosing a suspected Horner's pupil.