Argyll Robertson pupil

Overview
Argyll Robertson pupils (“AR pupils”) are bilateral small pupils that constrict when the patient focuses on a near object (they “accommodate” with near vision), but do not constrict when exposed to bright light (they do not “react” to light). They were formerly known as "prostitute's pupils" because of their association with syphilis and because, like a prostitute, they “accommodate but do not react.” ).  They are a highly specific sign of neurosyphilis. Pupils that “accommodate but do not react” are said to show light-near dissociation.  A video of AR pupils and light-near dissociation is available at http://content.lib.utah.edu/u?/EHSL-Moran-Neuro-opth,60

AR pupils are extremely uncommon in the developed world. There is continued interest in the underlying pathophysiology, but the scarcity of cases makes ongoing research difficult.

History
The AR pupil was named after Douglas Moray Cooper Lamb Argyll Robertson, a Scottish ophthalmologist who noted the association with syphilis in 1869. When serological tests for syphilis became available, patients with AR pupils usually tested positive for syphilis. The AR pupil became known as a reliable clinical sign of syphilis.

In the early 20th century, Adie described a second type of pupil that could “accommodate but not react.” Adie’s tonic pupil is usually associated with a benign peripheral neuropathy (Adie syndrome), not with syphilis.

When penicillin became widely available in the 1940s, the prevalence of AR pupils (which develop only after decades of untreated infection) decreased dramatically. AR pupils are now quite rare. A patient whose pupil “accommodates but does not react” almost always has a tonic pupil, not an AR pupil.

In the 1950s, Loewenfeld distinguished between the two types of pupils by carefully observing the exact way in which the pupils constrict with near vision. The near response in AR pupils is brisk and immediate. The near response in tonic pupils is slow and prolonged.

Pathophysiology
The two different types of near response are caused by different underlying disease processes. Adie's pupil is caused by damage to peripheral pathways to the pupil (parasympathetic neurons in the ciliary ganglion that cause pupillary constriction to bright light and with near vision). The AR pupil is thought to be caused by damage to central pathways for pupillary constriction. Specifically, the AR pupil is thought to be caused by selective damage to pathways from the retina to the Edinger-Westphal nucleus. These light-sensitive pathways allow the pupil to constrict to bright light. The accommodation pathways – pathways to the Edinger-Westphal nucleus that cause the pupils to constrict with near vision – are thought to be spared because of their more ventral course in the brainstem.

The exact relationship between syphilis and the two types of pupils (AR pupils and tonic pupils) is not known at the present time. The older literature on AR pupils did not report the details of pupillary constriction (brisk vs. tonic) that are necessary to distinguish AR pupils from tonic pupils. Tonic pupils can occur in neurosyphilis. It is not known whether neurosyphilis itself (infection by Treponema pallidum) can cause tonic pupils, or whether tonic pupils in syphilis simply reflect a coexisting peripheral neuropathy.

Thompson and Kardon (2006) summarize the present view:


 * The evidence supports a midbrain cause of the AR pupil, provided one follows Loewenfeld’s definition of the AR pupil as small pupils that react very poorly to light and yet seem to retain a normal pupillary near response that is definitely not tonic.


 * To settle the question of whether the AR pupil is of central or peripheral origin, it will be necessary to perform iris transillumination (or a magnified slit-lamp examination) in a substantial number of patients who have a pupillary light-near dissociation (with and without tonicity of the near reaction), perhaps in many parts of the world.

Parinaud syndrome
A third cause of light-near dissociation is Parinaud syndrome, also called dorsal midbrain syndrome. This uncommon syndrome involves vertical gaze palsy associated with pupils that “accommodate but do not react.” The causes of Parinaud syndrome include brain tumors (pinealomas), multiple sclerosis and brainstem infarction.

Due to the lack of detail in the older literature and the scarcity of AR pupils at the present time, it is not known whether syphilis can cause Parinaud syndrome. It is not known whether AR pupils are any different from the pupils seen in other dorsal midbrain lesions.