Argyll Robertson pupils
Argyll Robertson pupils
Description, Causes and Risk Factors:
A form of reflex iridoplegia characterized by miosis, irregular shape, and a loss of the direct and consensual pupillary reflex to light, with normal pupillary constriction to a near vision effort (light-near dissociation); often present in tabetic neurosyphilis.
The Argyll Robertson pupil, a miotic pupil that responds to an accommodation effort but fails to react to direct light, has been described in medical literature for more than a century. This pupillary reaction (Sidebar) is a simple way to confirm the integrity of the optic pathways and is a marker of such neurological disorders as neurosyphilis, neurosarcoidosis, and multiple sclerosis. The test requires no special equipment, holds great diagnostic yield, and takes less time to elicit than is needed to pronounce the eponym.
In an Argyll Robertson pupil, the pupil's better response to accommodation than to light stimuli occurs because the lesion involves the more dorsally located fibers that subserve the pupil's response to light. The lesion spares the more ventrally located fibers that subserve the pupil reaction to near stimuli.
In 1869, Douglas Argyll Robertson was the first to describe several patients whose pupils reacted poorly to light with a normal near response. It wasn't until 30 years later that physicians realized the etiology of this pupillary anomaly was a manifestation of tertiary syphilis. Most descriptions of the Argyll Robertson pupils do not mention segmental iris sphincter constriction, or slow, sustained constriction with a near vision effort. Such features are considered typical of the light-near dissociation of Adie syndrome and of neuropathic tonic pupils, where damage to the ciliary ganglion or ciliary nerves is believed to be the mechanism. Because the Argyll Robertson pupils lack these features, it has been attributed to a dorsal midbrain lesion that interrupts the pupillary light reflex pathway but spares the more ventral pupillary near reflex pathway. However, lesions in this region have not been reliably demonstrated in syphilis.
The pathophysiologic mechanism which produces an Argyll Robertson pupil is unclear. Studies have failed to demonstrate a focal localizing lesion. Research has implicated the rostral midbrain in the vicinity of the sylvian aqueduct of the third ventricle as the most likely region of damage. A lesion in this area would involve efferent pupillary fibres on the dorsal aspect of the Edinger-Westphal nucleus (associated with the response to light) while sparing the fibres associated with the response to near, which lie slightly more ventrally.
Argyll Robertson pupil should not be confused withAdie's pupil, which may yield a similar result on cursory examination. In Adie's pupil, which is caused by ciliary ganglion destruction, the reaction to light is absentor greatly diminished when tested in the routine examination; however, Adie's pupil does react slowly withprolonged maximal stimulation. Furthermore, oncethe Adie's pupil reacts to accommodation, the pupiltends to remain tonically constricted and dilates veryslowly.
The pupillary findings consistent withArgyll Robertson pupils develop over thecourse of months to years. The abnormalityin pupillary function begins with a sluggishresponse to light and eventually progressesto a complete loss of the light reflex. The irisatrophies with a loss of its radial folds, and crypts have been reported.
Patients who present with miotic pupilsshould be further assessed for ArgyllRobertson pupil. The detection of thispupillary anomaly is significant and requiresimmediate referral for neurological, physicaland laboratory evaluations. The systemicmanifestations associated with thiscondition carry life impactingconsequences. The earlier a firm diagnosiscan be made, the better the prognosis will befor the patient. Once a diagnosis isestablished, treatment should be swift andpotent in order to eradicate the infectiousorganism and prevent organ degradation.Practitioners play a critical role in thedetection, management and treatment ofthis disease.
Resolving the issue about the location of the syphilitic lesion that produces the Argyll Robertson pupilswill depend on careful examination of patients with techniques designed to disclose segmental palsy of the iris. If segmental iris sphincter palsy is found and the light-near dissociation has tonic features, one must conclude that the mechanism of the pupil disorder is a ciliary (peripheral) rather than a midbrain (central) denervation. Until better evidence settles the localization of the Argyll Robertson pupils, it is appropriate to screen patients with bilateral tonic pupils for syphilis.
There is no known treatment. Syphilis is the major cause of Argyll Robertson Pupil and hence it should be treated in priority. Administration of penicillin intravenously is the method to treat almost all stages of syphilis. Doxycycline or tetracycline can be used as alternative medicine. Once treatment has begun, patients can be followed using the rapid plasma reagin [RPR] test. Because the RPR measures the level of antibodies to cardiolipin and not antibodies to the treponema organism, the titer will vary based on the effectiveness of the treatment. Once the individual is infected with the organism, both the FTA-ABS or the MHA-TP will always remain positive since it detects the presence of antibodies toward the treponema organism.
NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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