involvement suggests a less emergent condition and can be approached in a more relaxed fashion, particularly when the patient is older and has associated risk factors for small vessel disease. This association is due to the anatomy of the autonomic portion of the oculomotor nerve within the subarachnoid space. The preganglionic fibers are situated on the external surface of the nerve, where they are easily damaged by compressive lesions that put mechanical pressure on the nerve. Ischemia caused by nonperfusion of a small vessel supplying blood to the core of the nerve, as is common in patients with diabetes and/or hypertension, is more likely to spare the autonomic fibers, since the smaller autonomic fibers have lower metabolic requirements and are in closer contact with the cerebrospinal fluid, receiving their oxygen supply in part through the cerebrospinal fluid and in part from vessels lying directly on the external surface of the nerve.
Aberrant regeneration, in which the pupil constricts in response to (most commonly) attempted adduction or depression, is a clear sign of oculomotor paresis by a mechanical mechanism, such as by trauma or by compressive lesions. The damaged axons reinnervate the extra ocular muscles in a disorganized way, causing a pathological synkinesis. The upper lid is also affected in many cases, producing a retraction of the upper lid in response to attempted adduction or depression (often called a pseudo-von Graefe sign). If aberrant regeneration develops gradually in
The cause is most commonly a pinealoma with compression of the quadrigeminal plate from above, also causing obstruction of cerebral spinal fluid flow and signs of papilledema. Lesions arising within the midbrain (usually among older patients) are usually ischemic in nature and can cause more widespread damage, with complex neurological deficits.
Detection of the clinical signs of this syndrome mandates imaging of the midbrain and the surrounding structures.
Mechanically distorting lesions of the iris are easily identified at the slit lamp. One can find even subtle tears in the iris sphincter with associated loss of the of the pupil's circular shape. An attack of angle closure glaucoma typically causes a mid-dilated pupil that is unresponsive to a light stimulus. Unintended topical application of parasympatholytic agents (a so-called pharmacologic pupil) can be confirmed by instillation of 1% pilocarpine, which will have no effect on the size of the pupil. The cause is usually either contact with a pharmacologic agent or exposure to plant materials containing scopolamine (■ Fig. 5.7).
Uncommon Pupillary Disturbances
Argyll-Robertson pupils are characterized by bilateral miosis, no responses to light stimuli, a preserved near response, and little or no response to mydriatics. They have been reported in cases in the late stages of tertiary neurosyphilis. We have seen many cases that mimic this appearance, but in which segmental pupil sphincter activity clearly labeled them as long-standing cases of tonic pupillary syndrome. Serological tests for luetic disease were negative in all instances. In those cases that suggest the diagnosis of Argyll-Robertson pupils, a fluorescent treponemal antibody absorption test (FTA-abs) test should be done, although the probability of a positive finding is low.
Intermittent Mydriasis Definition
Intermittent mydriasis appears as an abrupt enlargement of the pupil, lasting 5 to 60 min, and it is unasso-ciated with signs of visual loss.
The diagnosis of intermittent mydriasis (■ Table 5.3) is complicated by the absence of findings at the time of the examination, including normal pharmacologic tests of pupil function. It is very unlikely that these episodes will be linked to any credible threat to the patient's vision. When
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