Argyll Robertson Pupils

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Disease

Argyll Robertson pupils, also known as AR pupils, are characterized by small and irregular pupils that have little to no constriction to light but constricts briskly to near targets. The affected pupils initially appear small, and are irregular, but as opposed to the tonic pupil do not maintain increased tone to near targets. The pupils are noticeably able to accommodate near targets, with subsequent normal and brisk redilation to far.[1]

The characteristic light-near dissociation of AR pupils occurs most often bilaterally but may be unilateral in some patients.[2] In addition, AR pupils are accompanied with frequent iris atrophy. [3] Douglas Moray Cooper Lamb Argyll Robertson, a Scottish ophthalmologist and surgeon, originally described this abnormal pupil finding in 1868.[1]

Epidemiology

Argyll Robertson pupils were originally described with neurosyphilis and the finding became a characteristic clinical sign for the disease. However, with the efficacy of penicillin for the treatment of syphilis, the incidence of tertiary syphilis has decreased, and Argyll Robertson pupils have become quite rare in the United States. As the prevalence of syphilis has decreased to 2.1 per 100,000 population in the year 2000, the percentage of non-syphilitic AR pupil findings have increased.[4][5] Bilateral tonic pupils are more likely than AR pupils in the modern era.

Pathophysiology

Damage to the rostral midbrain can result in Argyll Robertson pupils. Specifically, a lesion of the rostral midbrain within the dorsal aspect of the Edinger-Westphal nucleus can interrupt the pretectal oculomotor light reflex fibers. However, the more ventrally located fibers of the Edinger-Westphal nuclei that control the near reaction are spared.[2]

Supranuclear adrenergic fibers that inhibit the Edinger-Westphal nucleus are necessary for iris sphincter relaxation and pupil dilation. When this inhibitory pathway is disrupted, parasympathetic neurons of the Edinger-Westphal nucleus that naturally fire at a high rate can lead to sustained pupil contraction by the iris sphincter and cause miosis in AR pupils.[5]

The damaging lesion in Argyll Robertson pupils usually develops over a period of time, sometimes asymmetrically and sometimes at an uneven rate. During this period, the pupillary light reactions progress from slow, incomplete constrictions to complete loss of the light reflex.[5]

Causes

Although Argyll Robertson pupils are classically associated with neurosyphilis, other AR like pupils can occur in diabetes mellitus, neurosarcoidosis, chronic alcoholism, encephalitis, multiple sclerosis, Lyme disease, or herpes zoster.[1][2]

Exam

Patients with Argyll Robertson pupils typically present with miotic pupils (<2mm in diameter) that do not dilate fully in dim light.[1][3] Upon close examination, pupils present with an irregular shape and can sometimes be described as oval, egg-shaped, tear shaped, irregularly polygonal, serrated, or eccentric.[5] Examination of the pupils also reveal minimal or complete absence of pupillary constriction to light stimulation. However, there is brisk pupillary constriction for accommodation to near targets and brisk redilation after the near reaction, which distinguishes AR pupils from Adie tonic pupils. This light-near dissociation is bilateral in 80-90% of patients, but both pupillary size and degree of light-near dissociation can be asymmetric.[5] Over time, Argyll Robertson pupils eventually lose their near constriction as well and become miotic, immobile pupils.[5] Slit lamp exam of the pupil often shows iris atrophy along with transillumination in portions of the iris. Additionally, pupils will demonstrate poor dilation after mydriatic eyedrop administration.[3]

Diagnostic procedures

It is important to check patient history for diabetes, trauma, and other neurologic diseases. All patients with bilateral tonic pupils should be considered for serologic testing for syphilis.[6]

Differential diagnosis

Although Argyll Robertson pupils are strongly associated with neurosyphilis, diagnoses for similar representations of light-near dissociation should also be considered [1]:

1) Adie’s tonic pupil

2) Afferent light near dissociation (optic nerve or severe retinal disease OU). These pupils will not be small and will not show iris abnormalities or irregularity.

3) Dorsal midbrain syndrome (Parinaud Syndrome, Sylvian Aqueduct Syndrome, Pretectal Syndrome)

4) Aberrant regeneration of the third nerve

Management

Management should be aimed at treating the primary cause of the pupillary abnormality.

References

  1. 1.0 1.1 1.2 1.3 1.4 McGee S. The Pupils. In: Evidence-Based Physical Diagnosis. 4th ed. Philadelphia, PA: Elsevier; 2018;161-180.e3. https://doi.org/10.1016/B978-0-323-39276-1.00021-4
  2. 2.0 2.1 2.2 Smith S, Lee AG, Brazis PW. Anisocoria and Pupillary Abnormalities. In: Clinical Pathways in Neuro-ophthalmology: An Evidence-Based Approach. 3rd ed. New York, NY: Thieme; 2019; 1344-1391.
  3. 3.0 3.1 3.2 Bhatti TM, et al. The Patient with Pupillary Abnormalities. In: 2018-2019 Basic and Clinical Science Course, Section 05: Neuro-Ophthalmology. San Francisco, CA: American Academy of Ophthalmology; 2019; 284-297.
  4. “Syphilis”. Centers for Disease Control and Prevention, https://www.cdc.gov/std/stats17/syphilis.htm. Accessed 20 May 2020.
  5. 5.0 5.1 5.2 5.3 5.4 5.5 Miller NR, et al. Disorders of Pupillary Function, Accommodation, and Lacrimation. In: Walsh and Hoyt’s Clinical Neuro-Ophthalmology. 6th ed. Philadelphia, PA: 2005; 739-805.
  6. Thompson HS. Adie’s syndrome: some new observations. Trans Am Ophthalmol Soc 1977; 75:587- 626.