Another interesting pupillary abnormality is the tonic reaction, also referred to as the Adie pupil. This syndrome is caused by a degeneration of the ciliary ganglia and the postganglionic parasympathetic fibers that normally constrict the pupil and effect accommodation. The patient may complain of unilateral blurring of vision or photophobia or may have noticed that one pupil is larger than the other. At the outset of the syndrome, the affected pupil is slightly enlarged in ambient light and the reaction to light is absent or greatly reduced if tested in the customary manner, although the pupil will slowly constrict with prolonged bright light stimulation. Characteristically, there is a light-near dissociation, that is, like the Argyll Robertson pupil, the Adie pupil responds better to near (accommodation) than it does to light. The most characteristic feature is that once the pupil has constricted, it tends to remain tonically constricted and redilates very slowly (the “tonic” aspect of the syndrome). Once dilated, the pupil remains in this state for many seconds, up to a minute or longer. Paralysis of a segment or segments of the pupillary sphincter is also characteristic of the syndrome; this segmental irregularity can be seen with the high plus lenses of an ophthalmoscope. The affected pupil constricts promptly in response to the common miotic drugs and, due to denervation supersensitivity, is unusually sensitive to a 0.1 percent solution of pilocarpine, a concentration that has only minimal effect on a normal pupil.
The tonic pupil usually appears during the third or fourth decade of life and is much more common in women than in men; it may be associated with absence of knee or ankle jerks (Holmes-Adie syndrome) and hence be mistaken for tabes dorsalis. From all available data, it represents a special form of mild inherited polyneuropathy. There can be a familial tendency to the syndrome. We have observed it as an accompaniment of a diffuse ganglionopathy associated with Sjögren disease, other autoimmune or paraneoplastic illnesses, and following recovery from the Guillain-Barré syndrome.
This rare pupillary phenomenon is characterized by transient episodes of unilateral mydriasis for which no cause can be found (the springing pupil). Episodes of mydriasis, which are more common in women, last for minutes to days and may recur at random intervals. Oculomotor palsies and ptosis are not present. Sometimes the pupil is distorted into an ovoid or tadpole shape during the attack. Some patients complain of blurred vision and head pain on the side of the mydriasis, suggesting an atypical ophthalmoplegic migraine. In children, following a minor or major seizure, one pupil may remain dilated for a protracted period of time. The main consideration in an awake patient is that the cornea has inadvertently (or purposefully) been exposed to mydriatic solutions, among them bronchodilator drugs, scopolamine, and some organophosphate pesticides.
Differential Diagnosis of Anisocoria (Fig. 13-11)
In regard to pupillary disorders, there are two main issues with which the neurologist has to contend. One is the problem of unequal pupils (anisocoria), and determining whether this abnormality is derived from sympathetic or parasympathetic denervation. The second problem is the relative afferent pupillary defect, and how to recognize it; this was discussed earlier.
In dealing with anisocoria, 20 percent of normal persons show an inequality of 0.3 to 0.5 mm or more in pupillary diameter. This is “simple,” or physiologic, anisocoria, and it may be a source of confusion in patients with small pupils. Its main characteristic is that the same degree of asymmetry in size is maintained in low, ambient, and bright light conditions. It is also variable from day to day and even from hour to hour, and often will have disappeared at the time of a second examination (Loewenfeld; Lam et al).