Bilateral Tonic Pupils in the Absence of Pupillary Cholinergic Supersensitivity

Goktas and Goktas¹ describe an intriguing case of a young woman with assumed bilateral tonic pupils in the absence of pupillary cholinergic supersensitivity. In the article, the lack of cholinergic supersensitivity is explained by reinnervation of the iris sphincter.

A tonic pupil occurs because of postganglionic parasympathetic denervation of the iris sphincter. The denervated segments show cholinergic supersensitivity to pilocarpine. Aberrant regeneration of accommodative fibres into the iris sphincter, called the reinnervation process, follows segmental denervation. Once the sphincter segments become reinnervated more completely by the accommodative fibres, the response to the cholinergic supersensitivity may diminish or resolve completely. Therefore, the degree of parasympathetic degeneration and regeneration of the efferent pupillomotor fibres influences the degrees of cholinergic supersensitivity and light-near dissociation.²

In this denervation-reinnervation process, there are two time periods where cholinergic supersensitivity is expected to be absent. Since cholinergic supersensitivity usually takes a few weeks to develop following postganglionic parasympathetic denervation, testing with 0.125% pilocarpine may fail to demonstrate cholinergic supersensitivity in this interval. The second time period is in the later stages of the denervation-reinnervation process, in which postganglionic nerves have grown back into the denervated sphincter segments. Once aberrant regeneration has taken place, the receptor’s sensitivity goes down and loses cholinergic supersensitivity.

This case presented by Goktas and Goktas¹ describes denervation followed by a reinnervation processes. The case demonstrates minimal reaction to light, no response to dilute pilocarpine, and a tonic response to accommodation, which probably indicates that denervated sphincter segments were reinnervated by accommodative fibres. However, further studies, which will demonstrate denervation and innervation of the iris sphincter, may yield a better understanding of this unusual clinical finding.

Furthermore, in contrast to idiopathic tonic pupils, bilateral tonic pupils with anisocoria of less than 1 mm usually indicate a generalised peripheral or autonomic neuropathy, paraneoplastic syndrome, or connective tissue disease.³ Therefore, anti-ganglioside antibodies and antineuronal antibodies, such as anti-Hu, anti-Yo, and anti-Ri, should be tested to identify the aetiology.

In conclusion, a lack of cholinergic supersensitivity is a rare but outstanding finding in cases of tonic pupil. Cholinergic supersensitivity provides useful information to clinicians regarding disorders of innervation of the iris sphincter.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.