The opposite of ptosis, that is, retraction of the upper lids, with a staring expression (Collier sign) is observed in thyroid disease, progressive supranuclear palsy, and hydrocephalus and other causes of the dorsal midbrain syndrome. In thyroid eye disease is the “lid-lag” refers to delayed relaxation of the eyelid on attempted downgaze (Von Graefe sign). Proptosis and ocular muscle restriction are present in the full form of the condition. PSP has prominent volitional vertical gaze abnormalities. In hydrocephalus, the downturning of the eyes is often referred to as the “sunset sign.” The elements of the dorsal midbrain syndrome have been described earlier in this chapter. The von Graefe sign on downward gaze is usually not present, in distinction to what is observed in thyroid ophthalmopathy. Slight lid retraction has been observed in a few patients with hepatic cirrhosis, Cushing disease, chronic steroid myopathy, and hyperkalemic periodic paralysis. Lid retraction can also be a reaction to ptosis on the other side; this is clarified by lifting the ptotic lid manually, and observing the disappearance of contralateral retraction as mentioned previously.
Myotonic dystrophy features ptosis as a component of the myopathic facies. In myotonia congenita, forceful closure of the eyelids may induce a strong aftercontraction. In certain extrapyramidal diseases, particularly progressive supranuclear palsy and Parkinson disease, even gentle lid closure may elicit blepharoclonus and blepharospasm on attempted opening of the lids; or there may be a delay in the opening of the tightly closed eyelids. Acute right parietal or bifrontal lesions often produce a peculiar disinclination to open the eyelids, even to the point of offering active resistance to forced opening. The closed lids give the false impression of diminished alertness and has incorrectly been called an apraxia of lid opening.
The testing of pupillary size and reactivity, which can be accomplished by the use of a flashlight and simple printed gauge, yields important, often vital clinical information. Essential, of course, is the proper interpretation of pupillary reactions, and this requires some knowledge of their underlying neural mechanisms.
The diameter of the pupil is determined by the balance of innervation between the constricting sphincter and radially arranged dilator muscles of the iris. The pupilloconstrictor (parasympathetic) fibers arise in the Edinger-Westphal nucleus in the high midbrain, join the third cranial (oculomotor) nerve, and synapse in the ciliary ganglion, which lies in the posterior part of the orbit. The postganglionic fibers then enter the globe via the short ciliary nerves. Only 3 percent of these fibers mediate pupillary constriction to light, while the remaining 97 percent are responsible constriction occurring as part of the near response during accommodation. The sphincter of the pupil comprises 50 motor units, according to Corbett and Thompson.
The pupillodilator (sympathetic) fibers arise in the posterolateral part of the hypothalamus and descend, uncrossed, in the lateral tegmentum of the midbrain, pons, medulla, and cervical spinal cord to the eighth cervical, and first and second thoracic segments, where they synapse with lateral horn neurons. The latter give rise to preganglionic fibers, most of which leave the cord by the second ventral thoracic root and proceed through the stellate ganglion to synapse in the superior cervical ganglion. The postganglionic fibers ascend along the internal carotid artery and traverse the cavernous sinus, where they join the first division of the trigeminal nerve, finally reaching the eye as the long ciliary nerves that innervate the dilator muscle of the iris. Some of the postganglionic sympathetic fibers also innervate the sweat glands and arterioles of the face, and Müller’s muscle in the eyelid.
The Pupillary Light Reflex