Horner syndrome: tribute to Professor Horner on his 190 th birthday

Abstract This paper reviews some aspects of the life and work of Professor Johann Friedrich Horner, on the occasion of the 190th anniversary of his birthday and 152 years after the publication of "Über eine Form von Ptosis". It also shows the importance of the historical description of ptosis, myosis and anhidrosis associating those symptoms with sympathetic cervical damage. He pharmacologically confirmed the impairment of sympathetic innervation to the eye and preserved parasympathetic function.

In 1869 Johann Friedrich Horner (Figure 1), a Swiss ophthalmologist, described the case of a 40-year-old woman with nonspecific headache, ptosis, myosis and right anhidrosis. He also noted a distinct flushing and warmth of the ipsilateral hemiface, observing that the patient was not sweating on that side of her face, which remained cold and pale. He also observed increased skin temperature and dryness of the ipsilateral face. There was no change in facial sensitivity showing integrity of the trigeminal nerve, with right vasomotor paralysis. He pharmacologically confirmed the impairment of sympathetic innervation to the eye after noting poor dilation of the affected pupil following instillation of atropine and preserved pupillary constriction to the parasympathomimetic agent calabar, containing physostigmine. He associated those symptoms with sympathetic cervical damage 1 .
The sympathetic pathway to the eye and its attachments is a three-neuron pathway, which begins in the central nervous system ( Figure 2). The first order neuronal fibers originate from the posterolateral hypothalamus. They descend through the brain stem to end at the spinal cord at the ciliospinal center (C8-T2). The second order (preganglionic) neuronal fibers leave the T1 root and travel close to the pulmonary apex through the paravertebral sympathetic chain and the stellate ganglion and end in the upper cervical ganglion. Tumors involving the upper lobe of the lung can interrupt the pathway at this level. Third-order (post-ganglionic) sympathetic fibers leave the ganglion to form a plexus around the internal carotid artery. Dissection of the internal carotid artery is a very important cause that can lead to interruption of the pathway at this level 2 .

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The plexus then rises to the cavernous sinus, and follows the ophthalmic division of the trigeminal nerve to the orbit, where it feeds the dilating muscles of the iris and the smooth muscle fibers of the upper and lower eyelids. The vasomotor fibers and the sweat glands to the face take a different course after leaving the ganglion. They follow the external carotid artery to supply half of the face on the same side. Horner syndrome (HS) can result from an interruption, at any level, of the sympathetic fibers supplying the eye and face 2 .
Diagnosis of HS is based on clinical observation but may be confirmed by pharmacological testing, as the prevailing features are readily apparent. They include miosis, partial ptosis, apparent enophthalmos and anhidrosis (Figure 3). Less constant to rare features include (on the affected side): facial flushing, arteriolar or venular dilatation (best seen in the retina), transient lowering of intraocular pressure, hemiatrophy of the face and iris heterochromia (in congenital HS). Visual acuity is rarely affected. Other symptoms and signs can be present due to compression of surrounding structures by the offending lesion 3 . The pupillary abnormality HS is an anisocoria with a smaller pupil on the affected side. This is best identified by comparing the degree of anisocoria in bright light and in darkness with the greatest degree of anisocoria expected 5−7s after the lights are turned off because of a deficiency of sympathetic tone to the dilator muscle in the affected eye.
Johann Friedrich Horner was the second child of Dr. Solomon Horner (1801-1852) and Magdalena Zellner In Paris he visited exponents of the area such as Broca and Desmarres, returning to Zurich in 1856. In 1862 he was appointed extraordinary professor, and in 1873 full professor. In more than 30 years of career he published 38 articles, the best known "Über eine Form von Ptosis" in 1869, like Horner curiosity does not add any reference in this paper1. In 1873, his student William Nicati published the thesis "La paralysie  du nerf sympathique cervical", in which a patient named Anna Brändli, previously described by Horner, returns as patient number 15. In the first chapter there is a historical introduction that clearly shows that the author was familiar with the content of the works of Claude Bernard and François Pourfour du Petit 4,5,6 .
According to Van der Wiel, "an impression about his character can be obtained by reading his autobiography, (...) he was very good with his poor patients, 50% of his private practice, who were treated free of charge. They were even admitted to his clinic, the Hottingerhof, where they were treated free of charge as well. He had an extremely good memory and could remember patients' faces for many years. Horner had a keen judgment of business and people, he did not allow himself to be ruled by emotions and focused on realistic goals" 4 .
Professor Horner was not only the founder of modern Swiss scientific ophthalmology but also the moving spirit behind improvements in social and medical affairs. Horner died at the age of 55, on December 20, 1886, after a stroke in the left hemisphere 4 .
Recognizing HS is critical, as those findings point to a lesion in the oculosympathetic pathway. Though often benign or idiopathic, the cause of HS can be very threatening or even lethal, so understanding how to recognize, diagnose, and appropriately evaluate HS is important to all clinicians 3 . Horner was the first one to give a detailed, scientifically supported account and to accurately interpret the signs of cervical sympathetic nerve damage in a human subject.
Our aim is to draw attention to HS and to paye a modest tribute to the 19th century master of neuro-ophthalmology for the 190th anniversary of his birthday.