Which of the following pupillary findings is characteristic of Argyll Robertson pupil?

Explanation

## Argyll Robertson Pupil: Definition and Mechanism **Key Point:** Argyll Robertson pupil is characterized by **loss of light reflex with preserved accommodation reflex** — a dissociated pupillary response. ### Pathophysiology The lesion affects the pupillary light reflex pathway (pretectal nucleus and Edinger-Westphal nucleus connections) while sparing the accommodation pathway (medial longitudinal fasciculus and ciliary ganglion). This selective damage results in: - **No pupillary constriction to light** (afferent or efferent arc disrupted) - **Normal pupillary constriction to accommodation** (accommodation pathway intact) ### Classic Associations | Association | Notes | | --- | --- | | **Neurosyphilis (most common)** | Particularly tertiary syphilis and general paresis of the insane (GPI) | | **Diabetes mellitus** | Rare but documented cause | | **Sarcoidosis** | Granulomatous inflammation affecting pupillary pathways | | **Amyloidosis** | Autonomic neuropathy involvement | **High-Yield:** In the Indian context, neurosyphilis remains an important cause of Argyll Robertson pupil, though diabetes-related autonomic neuropathy is increasingly recognized. ### Additional Features - Pupils are typically **small** (miotic) - Pupils may be **irregular** in shape - **Bilateral** presentation is common - **Slow or sluggish** accommodation response (even though present) **Clinical Pearl:** The mnemonic **"AR pupil = Accommodation Reflex present, light Reflex absent"** helps distinguish this from other pupillary pathologies. ### Differential from Other Pupillary Disorders | Condition | Light Reflex | Accommodation Reflex | Pupil Size | | --- | --- | --- | --- | | **Argyll Robertson** | Absent | Present | Miotic, irregular | | **Tonic pupil (Adie)** | Sluggish | Sluggish but present | Normal or dilated | | **Fixed pupil (3rd nerve palsy)** | Absent | Absent | Dilated | | **Horner syndrome** | Present | Present | Miotic | **Warning:** Do not confuse Argyll Robertson pupil with Adie's tonic pupil — the latter has sluggish (not absent) light reflex and very slow accommodation.