Pilocarpine Should Not Be Used to Diagnose Postoperative Anisocoria

Abstract

To the Editor: Although we read with interest the article by Sitzman et al., [1] on postoperative anisocoria, we have significant concern over the diagnostic test proposed. That phenylephrine-induced mydriasis can be differentiated from an intracranial neurologic emergency is readily understood. A centrally denervated pupil has a normal or supranormal response to direct cholinergic stimulation [2]. A pupil directly dilated with phenylephrine incompletely constricts to a minimum dose of pilocarpine [3]. Sitzman et al. were successful in demonstrating that this test could used perioperatively and discussed clearly the pharmacology and physiology involved. However, the fact that this can be done does not mean that it should be done. Because the parasympathetic component of cranial nerve (CN) III is dispersed peripherally around the nerve, pupillary dilation is an early indication of third nerve compression [4] and is one of the most important signs of impending herniation of the uncus through the tentorium. Complete palsy of CN III, with the pupil not only dilated but deviated laterally and inferiorly, is a late sign that signifies grave prognosis. To pharmacologically induce miosis in an earlier stage of CN III compression takes away a critically important indicator. The pupillary examination needs to be evaluated early and regularly after central neurosurgery or closed head trauma and may be the only clinical neurological assessment that can be performed on the paralyzed perioperative patient [5]. Sitzman et al.'s results indicate that the test does not produce a significant differentiating response until 15-30 min have transpired [1], a time that could significantly affect outcome if mydriasis is, in fact, due to a transtentorial uncal herniation. Furthermore, the effects of pilocarpine are long acting and can affect any further pupillary examinations for some time. Finally, the multitraumatized patient, who may be likely to have a nasal intubation, is the type of patient who will most need close perioperative observation for signs of an intracranial bleed. Although the authors' concern that computed tomographic scans are "costly and time consuming" is laudable, placing pilocarpine in the eye of a patient who may or may not have a catastrophic neurological event progressing is not to be encouraged. Early diagnosis is mandatory and should be rigorously pursued with close clinical monitoring and appropriate imaging. Timothy L. Sternberg, DMD, MD Department of Anesthesia and Perioperative Medicine; Medical University of South Carolina; Charleson, SC 29425 Brian G. Cuddy, MD Department of Neurosurgery; Medical University of South Carolina; Charleson, SC 29425 Aljoeson Walker, MD Department of Ophthalmology and Neurology; Medical University of South Carolina; Charleson, SC 29425 We failed to obtain a response from Dr. Sitzman.