Symptoms and signs. Patients with Horner syndrome can present with a variety of symptoms and signs. Patients may be largely asymptomatic or they may complain of a droopy eyelid and blurry vision. The full Horner syndrome triad consists of ipsilateral miosis, anhidrosis of the face, and mild ptosis of the upper eyelid with reverse ptosis of the lower eyelid.8 The difference in pupil size is greatest 4 to 5 seconds after switching from bright to dim room illumination due to dilation lag in the miotic pupil from poor innervation.1
Although the classical triad of ptosis, miosis, and anhidrosis is emphasized in the literature, the full triad may not always be present.4 This variation is due to the anatomy of the oculosympathetic pathway with branches of the nerve system separating at the superior cervical ganglion and following different pathways along the internal and external carotid arteries, resulting in anhidrosis only in Horner syndrome caused by lesions to the first- or second-order neurons.4,5 Because of this deviation of the nerve fibers in the pathway, the presence of miosis and a slight ptosis in the absence of anhidrosis should still strongly suggest Horner syndrome.
In addition to the classic triad, Horner syndrome can present with other ophthalmic findings, including conjunctival injection, changes in accommodation, and a small decrease in intraocular pressure usually by no more than 1 to 2 mm Hg.4 Congenital Horner syndrome is unique in that it can result in iris heterochromia, with the lighter eye being the affected eye.4
Due to the long and circuitous nature of the oculosympathetic pathway, damage can occur due to a wide variety of conditions (Table) and can present with many neurologic findings.7
Localization of lesions. In Horner syndrome, 13% of lesions were present at first-order neurons, 44% at second-order neurons, and 43% at third-order neurons.7 While all these lesions have similar clinical presentations that can be difficult to differentiate, localization of the lesion within the oculosympathetic pathway is important to determine the underlying cause. This determination can be readily achieved in office with pharmacologic pupil testing (Figure 3).
