Anisocoria — abnormally small pupil (horner syndrome)

A 46-year-old man presented with a two-week history of acute-onset left upper eyelid drooping. He also had left eye, ear, and neck pain, as well as numbness and pain along his left cheek. He denied trauma and was not taking any medications or eye drops. The remainder of his medical and ocular history was unremarkable. Best-corrected visual acuity was 20/20 in both eyes (OU). External exam showed left upper eyelid ptosis of 2 mm. There was no upside-down ptosis. In the dark, his right pupil measured 6 mm and his left pupil measured 4 mm with a dilation lag in the left eye (OS) with the lights dimmed. In the light, the right pupil measured 3 mm and the left pupil measured 1.5 mm (see Fig. 1.1). There was no relative afferent pupillary defect or light-near dissociation. Extraocular motility, intraocular pressure measurements, and slit lamp examination were normal OU. One drop of topical apraclonidine 0.5% was administered OU. After 30 minutes, the left ptosis improved, and the previously larger right pupil was now smaller and the previously smaller left pupil was now larger (see Fig. 1.2). Dilated fundus exam was normal OU. Corneal sensation and facial sensation in the V₁ and V₂ distributions were normal. Magnetic resonance imaging (MRI) of the face, orbits, head, and neck down to the level of the second thoracic vertebra revealed hyperintense signal intensity in the wall of the distal left internal carotid artery (i.e., the crescent sign) consistent with a left carotid dissection (see Fig. 1.3). Magnetic resonance angiogram (MRA) of the head and neck confirmed a dissection of the distal left cervical internal carotid artery (ICA) (see Fig. 1.4).