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Pupil Examination in Autonomic Neuropathy
Careful pupil examination detects abnormalities with varying prevalence in several neuropathic disorders.
Since antiquity, the eyes have been considered windows into the soul. Now, new findings suggest that they are also windows into the autonomic nervous system. The researchers used infrared pupillography to assess pupil responses in 150 patients (cases) with symptomatic autonomic neuropathy due to various disorders: amyloidosis, pure autonomic failure (PAF), diabetes, multisystem atrophy (MSA), and miscellaneous conditions, including paraneoplastic syndrome and hereditary neuropathies. The researchers compared the findings in cases with those in 315 age- and sex-matched healthy controls.
Two thirds of the cases had pupillary abnormalities attributable to autonomic dysfunction, compared with 4.6% of the controls. The authors teased apart the different manifestations of autonomic pathology: miosis in darkness, mydriasis in bright light, darkness anisocoria, bilateral tonic pupils, bilateral or unilateral Horner syndrome, reduced near reflex, and reduced light reflex. Common features of diabetic autonomic neuropathy were bilateral miosis in the dark, tonic pupils, poor response to light, and dissociation of light and near reflexes. These features were less common in amyloidosis and rare in PAF. They were not found in MSA, perhaps, the authors speculated, due to this condition’s central rather than peripheral pathology. Abnormal pupil responses were not significantly associated with systemic dysautonomic signs. Most patients’ deficits (85%) were bilaterally symmetric. Surprisingly, sympathetic pupillary deficits were twice as common as were parasympathetic deficits. Most patients had a combination of sympathetic and parasympathetic deficits.
Comment: In neurophysiologic terms, applying light to the pupils is equivalent to striking major tendons with a reflex hammer: We harvest concrete information, not otherwise obtainable at the bedside, about the condition of proximal and distal neurons and axons. These findings remind us that ophthalmologic abnormalities go beyond simply "sluggish pupils." Arguably, primary care practitioners cannot feasibly keep all the patterns of pupil dysfunction in mind, but specialists should do so when examining patients who have abnormal pupillary reflexes.
— Misha Pless, MD
Dr. Pless is Director, Division of General Neurology and Neuro-ophthalmology, Department of Neurology, Massachusetts General Hospital, and Associate Professor, Harvard Medical School, Boston.
Published in Journal Watch Neurology November 7, 2006
Citation(s):
Bremner F and Smith S. Pupil findings in a consecutive series of 150 patients with generalised autonomic neuropathy. J Neurol Neurosurg Psychiatry 2006 Oct; 77:1163-8.
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