Which Light Near Dissociation is primarily caused by a lesion of the ciliary ganglion?

• A. Tonic Pupil
• B. Argyll Robertson Pupil
• C. Adie's Pupil
• D. Horner's Syndrome

Answer: (A)

Light near dissociation arises when parasympathetic input to the iris sphincter is disrupted along the postganglionic pathway to the ciliary muscle. The ciliary ganglion is the relay point for this parasympathetic supply. When it is damaged, the pupillary light reflex is markedly reduced or absent because the sphincter cannot constrict in response to light, while the near response can remain relatively better preserved, producing constriction with accommodation. This pattern is characteristic of a tonic pupil, also known as Adie’s pupil, which reflects a ciliary ganglion lesion.

Argyll Robertson pupil results from a different problem in the pretectal area (neurosyphilis) and can show light–near dissociation as well, but not due to ciliary ganglion damage. Horner’s syndrome involves sympathetic pathway loss, causing miosis with ptosis and an anisocoria that is more pronounced in darkness, rather than the classic light–near dissociation pattern.