Argyll Robeson pupil results from the lesion of
**Core Concept**
Argyll Robertson pupil is a clinical sign characterized by bilateral, small, irregular pupils that constrict in response to near vision but not in response to light. This phenomenon is often associated with neurosyphilis, particularly in its tertiary stage.
**Why the Correct Answer is Right**
Argyll Robertson pupils result from lesions affecting the Edinger-Westphal nuclei in the midbrain, which are responsible for the parasympathetic control of the pupils. These nuclei are involved in the pupillary light reflex, but not the pupillary accommodation reflex. In neurosyphilis, inflammation and damage to these nuclei disrupt the pupillary light reflex, leading to the characteristic Argyll Robertson pupils. The preservation of the pupillary accommodation reflex is thought to be due to the relatively spared involvement of the ciliary ganglion.
**Why Each Wrong Option is Incorrect**
**Option A:** Lesions affecting the ciliary ganglion would result in impaired pupillary accommodation reflex, not preserved.
**Option B:** Damage to the oculomotor nerve (CN III) would result in ptosis, pupillary dilation, and impaired extraocular movements, not Argyll Robertson pupils.
**Option C:** Lesions affecting the pretectal nuclei would result in impaired pupillary light reflex, but would also affect the pupillary accommodation reflex, not preserving it.
**Clinical Pearl / High-Yield Fact**
In neurosyphilis, Argyll Robertson pupils are a classic sign that can be remembered using the mnemonic "Small, irregular pupils, in response to near, not to light."
**Correct Answer:** C.