Paralysis of the external rectus is quite common, and is either transient or permanent. The former variety is often put down as rheumatic, when it is really a symptom of tabes dorsalis. The permanent paralysis is frequently an accompaniment of the affections of the base of the brain: when these are located in the middle fossa of the skull it is often associated with paralysis of the facial. If hemiplegia be present, the lesion is usually situated farther back toward the exit of the nerve from the pons. Graux264 and Ferréol have called attention to a form of paresis which results from disease of the nucleus of the sixth pair. In this form, owing to the affection of the filament which the nucleus of the sixth nerve gives to the nucleus of the third nerve, which is distributed to the internal rectus of the other side, the amount of the secondary deviation is much diminished, and there is more or less the appearance of an ordinary concomitant convergent squint (where, as is well known, the excursions of the two eyes are nearly equal). In one case, where the autopsy showed that a small tubercle had been developed at the junction of the medulla and pons, just beneath the surface of the fourth ventricle, there was no other symptom than this conjugate deviation of the eyes. In another case, in which there was hemiplegia (hemiplégie alterne), a tubercle was found higher up in the pons, bulging into the fourth ventricle. In addition to the conjugate deviation of the eyes already mentioned, Graux and Ferréol believe that this central form of paralysis is distinguished by its gradual access, slow development, and persistence. They say that in pure cases of lesion of the nucleus it is characterized by the absence of all other symptoms, and still further assert that in those cases in which it is but partially involved the accompanying symptoms are either complete facial paralysis or alternate hemiplegia.
264 Thèse de Paris.
Affections of the Seventh Pair.
Loss of power in the orbicularis palpebrarum, and consequent lagophthalmos, is frequently encountered as part of paralysis of the facial nerve. Where the paralysis is complete, it prevents closure of the eyelids. Variation in the size of the palpebral fissure is, however, by no means abolished, for, owing to relaxation of the levator palpebrarum, the fissure diminishes when the patient looks down, but is increased by the activity of this muscle when he looks up.
BLEPHAROSPASM.—Spasmodic closure of the lids is frequent in phlyctenular conjunctivitis and in many corneal and conjunctival affections. It is evidently reflex in its origin, and often entirely out of proportion to the amount of conjunctival or corneal disease. A foreign body under the lids will frequently give rise to a similar state of reflex spasm. We also encounter a greater or less degree of twitching of the lids as part of general or local chorea.
Affections of the Twelfth Pair.
BULBAR PARALYSIS, LABIO-GLOSSAL LARYNGEAL PARALYSIS.—Affections of the eye and its appendages are rather exceptional in this form of disease. In one case Galezowski describes unilateral atrophy of the optic nerve, and Dianoux265 bilateral atrophy in another. In the latter the atrophy came on after partial paralysis of the lips and of the muscles of deglutition, it being preceded by paralysis of the right external rectus. Hallopeau266 quotes a case from Wachsmuth where there was partial paralysis of the facial which rendered the face immobile and effaced its wrinkles, allowing the lower lid to fall. He cites also a case of Hérard in which there was amblyopia and partial ptosis. He justly remarks that such phenomena indicate an extension of the lesion from the nucleus of the twelfth pair to other parts of the central nervous system. The pupils are sometimes described as contracted, more rarely as dilated. Leeser quotes Leube267 to the effect that "paralytic myosis, when it occurs in bulbar paralysis, is generally a sign that it is complicated either by progressive muscular atrophy or with sclerosis of the brain and spinal cord."
265 Quoted by Robin, Troubles oculaires dans les Maladies de l'Encephale, p. 335.
266 Des Paralysies bulbaires, Paris, 1875, p. 41.
267 Deutsches Archiv f. klin. Med., Bd. viii. pp. 1-19, quoted by Leeser, p. 94.