Argyll Robertson Pupil (ARP)
The Argyll Robertson pupil is small (miosis) and irregular. It fails to react to light (reflex iridoplegia), but does constrict to accommodation (when the eyes converge). In other words, there is light-near pupillary dissociation (ARP = accommodation reaction preserved). Since the light reflex is lost, testing for the accommodation reaction may be performed with the pupil directly illuminated: this can make it easier to see the response to accommodation, which is often difficult to observe when the pupil is small or in individuals with a dark iris. There may be an incomplete response to mydriatic drugs. Although pupil involvement is usually bilateral, it is often asymmetric, causing anisocoria.
The Argyll Robertson pupil was originally described in the context of neurosyphilis, especially tabes dorsalis. If this pathological diagnosis is suspected, a helpful clinical concomitant is the associated loss of deep pain sensation, as assessed, for example, by vigorously squeezing the Achilles tendon (Abadie’s sign). There are, however, a number of recognized causes of ARP besides neurosyphilis, including:
Hereditary motor and sensory neuropathies (Charcot-Marie Tooth disease; Dejerine-Sottas hypertrophic neuropathy)
Miosis and pupil irregularity are inconstant findings in some of these situations, in which case the term "pseudo-Argyll Robertson pupil" may be preferred.
The neuroanatomical substrate of the Argyll Robertson pupil is uncertain. A lesion in the tectum of the (rostral) midbrain proximal to the oculomotor nuclei has been claimed. In multiple sclerosis and sarcoidosis, magnetic resonance imaging has shown lesions in the periaqueductal gray matter at the level of the Edinger-Westphal nucleus, but these cases lacked miosis and may be classified as pseudo-Argyll Robertson pupil. Some authorities think a partial oculomotor (III) nerve palsy or a lesion of the ciliary ganglion is more likely.
Argyll Robertson D. Four cases of spinal myosis [sic]: with remarks on the action of light on the pupil. Edinburgh Medical Journal 1869; 15: 487-493 Dacso CC, Bortz DL. Significance of the Argyll Robertson pupil in clinical medicine. American Journal of Medicine 1989; 86: 199-202