Argyll Robertson Pupil

The pupil is an opening in the center of the eye that allows light to enter the eye. Typically, the pupil constricts, or shrinks, in response to bright light and dilates, or expands, in response to dim light. The Argyll Robertson (AR) pupil occurs when a disease interferes with the light reflex pathway, thereby inhibiting the pupil’s natural response to bright light. Specifically, Argyll Robertson pupils don’t constrict in response to light but do constrict to focus on a nearby object. The presence of Argyll Roberton pupils is typically a highly specific sign of tertiary syphilis; however, they can be caused by other underlying conditions, such as diabetes and multiple sclerosis.

The Argyll Roberston pupil was first described in the mid-1860s by Dr. Douglas Argyll Robertson, a Scottish ophthalmologist and surgeon. 

Tertiary syphilis is the most common cause of the Argyll Roberston pupil. Caused by a bacteria called Treponema pallidum, syphilis is typically transmitted sexually, but the infection can also occur transplacentally, from an infected pregnant individual to their fetus. Over time, untreated syphilis can become tertiary syphilis, a late-stage infection marked by damage to the Edinger-Westphal nucleus, the part of the pupillary light reflex pathway in the brain that signals the pupil to constrict in response to bright light.

Rarely, other conditions that affect the Edinger-Westphal nucleus are the source of AR pupils. For example, nerve damage due to diabetes or multiple sclerosis can take place in the light reflex pathway, which may cause AR pupils. Diabetes-related nerve damage occurs when blood sugar levels remain high for a long period of time, while multiple sclerosis involves autoimmune attacks on the protective layer around nerve cells. 

An Argyll Roberston pupil is rarely unilateral, or affecting only one eye. Typically, both of an individual’s eyes will have AR pupils, making the condition bilateral. 

A clinician can diagnose the Argyll Robertson pupil through a thorough evaluation of symptoms, conduction of a physical exam, and discussion of past medical history. The examination will typically show a light-near dissociation, in which the pupil focuses quickly on a near object but doesn’t respond to bright light. The clinician will also look for symptoms associated with the potential underlying causes of AR pupils, such as a lack of coordination and sudden, severe pains in the face, back, and limbs.

Other neurological signs that often accompany AR pupils include paresis and tabes dorsalis. Paresis refers to widespread brain tissue damage with symptoms affecting personality, reflexes, intellect, and speech. Tabes dorsalis is characterized by damage to neurons that affect their ability to transmit information, resulting in symptoms of bladder disturbances, impotence, and lack of coordination.

Individuals with AR pupils are often referred to clinicians who specialize in neuro-ophthalmology, which focuses on neurological causes of eye disease. A detailed examination of the eye may include a slit lamp examination. This procedure involves using a bright light and a microscope to assess for iris atrophy, or thinning of the colored part of the eye, a condition that often presents with AR pupils.

The slit lamp examination can also help to differentiate AR pupils from symptoms of Holmes-Adie syndrome. Holmes-Adie syndrome is characterized by tonic pupils, which are large and react slowly to light. The Adie tonic pupil is typically caused by damage to the ciliary ganglion, a bundle of nerves in the back of the eye.

After eye examinations, serologic testing of cerebral spinal fluid (CSF), the fluid that surrounds the brain and spinal cord, is often conducted in order to determine the presence of tertiary syphilis. A serology test requires a lumbar puncture or spinal tap, procedures that remove a sample of CSF by inserting a long needle into the lower back near the spinal cord. A diagnosis of diabetes can be confirmed or ruled out by performing a blood test called a Hemoglobin A1c. Finally, multiple sclerosis can be diagnosed using magnetic resonance imaging (MRI) of the brain.

Treatment for AR pupils depends on the underlying cause. Penicillin G, an antibiotic, is the treatment for tertiary syphilis, and it can be administered either into the veins (i.e., intravenously) or into muscle (i.e., intramuscularly). Typically, treatment of tertiary syphilis also includes oral probenecid, which increases penicillin levels in the individual’s body. If nerve damage due to diabetes is the cause, medications, such as antidepressants (e.g., duloxetine) or antiseizure medications (e.g., pregabalin), are generally prescribed. Multiple sclerosis can be treated with steroids initially, possibly followed by other medications, like glatiramer acetate, to prevent relapse of symptoms. 

The Argyll Roberson pupil is a small, abnormal pupil with impaired pupillary constriction in response to light. Argyll Robertson pupils are usually caused by tertiary syphilis, but they may also be caused by diabetes or multiple sclerosis. Usually, both of an affected individual’s eyes have AR pupils, but the condition may be present in only one eye on rare occasions. AR pupils are diagnosed through a medical examination, eye examination, and, depending on the suspected cause, various tests or imaging. Treatment depends on the underlying cause. In particular, tertiary syphilis is generally treated with a combination of penicillin G and probenecid.