The pupillary phenomenon of Argyll Robertson, or light-near dissociation, has been known since 1869, but its chief cause—syphilis—is as old as man. A light-sensitive retina and miosis are the essential features. An amaurotic eye also has a pupil that is rigid to direct light stimulation and that contracts to an imaginary target at near. The true Argyll Robertson pupil does contract to near but usually not normally. It is also smaller than a tonic pupil. A longstanding Adie's pupil may also become small but not as small as an Argyll Robertson pupil. The Argyll Robertson pupil is usually bilateral, but if it is initially unilateral, it is the smaller of the two pupils. Before-and-after pupil photographs under the same lighting mid distance fixation circumstances are important to accurately document the results of the examination.
Irregularity of the pupil, a phenomenon Frequently noted, is not one of the basic criteria. Argyll Robertson pupils become irregular because iritis occurs and posterior synechiae or iris atrophy from chronic inflammation develops. Argyll Robertson pupils also dilate poorly with atropine; however, this sign is difficult to evaluate and is not useful clinically.
The classic signs of Argyll Robertson pupil, therefore, are rigidity to light and contraction to accommodation. In the past, these signs indicated tertiary syphilis 99% of the time. Since the advent of antibiotics, however, syphilis is less prevalent, and light-near dissociation is now more commonly a sign of Adie's pupil or tonic pupils caused by diabetic or alcoholic neuropathies.
In the 1800s, the bright lights of the indirect ophthalmoscope or the slit lamp were not available. Many of the then light-rigid pupils perhaps would not be considered rigid today. Therefore, I prefer to use the criterion of light-near dissociation. The small amount that the pupil reacts to light is normal and not slow as in the tonic pupil.
The fact that Argyll Robertson pupil represents tertiary syphilis means that the usual blood tests may be negative. If they are, an PTA-ABS test should be done. Argyll Robertson pupil may be (and often 18) present without other signs of tertiary syphilis. Once syphilis is suspected, the physician should look for other ocular signs of the disease, such as peripheral chorioretinitls, if congenital syphilis is a possibility, the physician should look for salt-and-pepper retinopathy, as well as the ghost vessels of interstitial keyatitis. The ghost vessels should be looked for at the superior cornea beneath the upper lid, since they may be subtle and missed unless the lid is elevated when the slit lamp examination is performed.
Although the Argyll Robertson pupil has long been associated with tertiary syphilis, on rare occasions, it has been seen with herpes zoster, sarcoid, von Beonomo's encephalitis, diabetes, Lyme disease, Wernicke's encephalopathy. The exact location of the lesion has not been absolutely identified. However, a discrete lesion to the Edinger-Westphal nucleus in the area of the periaqueduct gray has been identified on magnetic resonance imaging (MRI) in cases of sarcoid and multiple sclerosis. The Edinger-Westphal nucleus has a caudal and a rostral area. The rostral portion controls the reflex to light, and the caudal portion regulates accommodation. A lesion in the rostral area would affect pupillary response and not accommodation, which is what we see in Argyll Robertson pupil, Tonic pupils also can occur in syphilis, The lesion In Adie's pupil is usually accepted as occurring in the postganglionic parasympathetic pathway. Recent cases of Thompson and Sharpe would suggest a similar she for syphilitic tonic pupil.
Mass lesions in and around the aqueduct of Sylvius, between the third and fourth ventricle, can cause Argyll Robertson pupils. The lesions frequently cause other signs, such as paralysis of up-gaze and retraction nystagmus. If retraction nystagmus is not obvious, it can be elicited by bringing optokinetic targets from, above down. In this way, the quick component of the nystagmus is up and reinforces the retraction nystagmus, which Is brought out in up-gaze or attempted up-gaze. The patient under consideration is obviously not a syphilitic patient.
Pseudo Argyll Robertson Pupil
Pseudo Argyll Robertson pupil is seen in pseudotabes pituitaria, pseudotabes diabetica, and third cranial nerve misdirection. In pseudotabes pituitaria, the light reaction is poor because of the underlying disease, in which the optic nerves are affected at the chiasm. In pseudotabes diabetica, the poor light reaction is secondary to either poor vision or neuropathy of the short ciliary nerves.
Third cranial nerve misdirection is not common, but it can be mistaken for unilateral Argyll Robertson pupil. It is the unilateral nature of the pseudo Argyll Robertson pupil that should bring third cranial nerve misdirection to mind. The pupillary reaction to near occurs not because the pupil contracts on near gaze but because the medial rectus muscle is stimulated on near gaze. The stimulation is due to a misdirection after recovery from third cranial nerve paralysis, in which some relationship develops between the medial rectus muscle and the pupillary fibers. The pupillary reaction can also be demonstrated by observing the pupil when the patient is looking at a distant point and turning his or her gaze to the right or left so as to stimulate the appropriate medial rectus muscle. This procedure causes contraction of the pupil, just as in convergence, and differentiates the condition from a true Argyll Robertson pupil. The significance of the sign is that it occurs more commonly after a traumatic third cranial nerve paralysis or because of an aneurysm and rarely with tumors or syphilis, and it has never been reported after diabetic third cranial nerve paralysis. Therefore, if a patient has third cranial nerve misdirection and diabetes, the previous third cranial nerve paralysis was caused not by the diabetes but by something else—in the absence of a history of severe trauma, most likely it is an aneurysm.
Some clinicians describe a pupil that is large and does not react to light but does contract to near (and is associated with a positive blood test) as an Argyll Robertson pupil.