hydroxyamphetamine) to localize the site of the lesion Table 29.4 summarizes the causes of acquired Horner syndrome in children All children who have Horner syndrome should receive a complete evaluation unless congenital Horner syndrome is known to be present, based on history, old photographs, and examination MYDRIASIS Local Factors Both trauma and topical agents can cause unilateral mydriasis Blunt trauma (and, less commonly, intraocular surgery) can result in a fixed dilated pupil Traumatic mydriasis usually occurs in a setting in which a clear history of trauma and other intraocular injuries, such as hyphema, are noted The pupil may be somewhat irregular in shape if the sphincter has irregular tears that appear as V-shaped notches in the pupil margin best seen using the direct ophthalmoscope as a magnifier Sometimes, pigment deposition can be seen on the anterior surface of the lens