Features of a tonic pupil include anisocoria that is greater in bright light and a pupil that is sluggishly and segmentally responsive to light and more responsive to near effort. Greater-than-normal constriction in response to dilute pilocarpine is diagnostic. Possible etiologic causes in children include varicella-zoster virus infection and Adie syndrome with absence of deep tendon reflexes.
A lesion at any location along the oculosympathetic pathway may lead to Horner syndrome. Affected patients have anisocoria that is greater in dim light and ptosis secondary to paralysis of the Müller muscle. Congenital cases may be associated with iris heterochromia in which the affected iris is lighter in color. However, the heterochromia may not be present in infants because the normal iris needs time to acquire pigment.
The diagnosis of Horner syndrome can be confirmed with the use of topical cocaine or apraclonidine drops. Apraclonidine reverses the anisocoria, causing dilation of the affected (smaller) pupil and having no effect on the normal pupil. This agent should be used with caution in young children, as it may cause excessive sedation owing to its central nervous system effects. Additional pharmacologic testing may not be necessary in the presence of typical clinical findings.
Horner syndrome in children may be idiopathic or may be caused by trauma, surgery, or the presence of neuroblastoma affecting the sympathetic chain in the chest. For children with acquired Horner syndrome but no history of trauma or surgery that could explain the anisocoria, evaluation should include imaging studies of the brain, neck, and chest. The value of measuring catecholamine excretion has been questioned because some patients with normal catecholamine measurements have been found to have neuroblastomas.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.