Pupil Assessment 10 Flashcards

A patient with bilateral symmetric optic neuropathy causing 20/200 vision in each eye undergoes swinging flashlight testing. Which finding is most expected?

Answer: No RAPD, because the afferent input to both eyes is equally reduced

RAPD is a relative test — it measures asymmetry between the two eyes' afferent inputs. In bilateral, symmetric optic neuropathy, even with severe vision loss, both pupils receive equally degraded signals, so no RAPD is detected. The absence of RAPD does not rule out bilateral optic nerve disease.

Hydroxyamphetamine (Paredrine) 1% is instilled in a patient with confirmed Horner syndrome. Thirty minutes later, the affected pupil fails to dilate. What does this indicate?

Answer: The lesion involves the third-order (postganglionic) neuron

Hydroxyamphetamine works by releasing stored norepinephrine from intact third-order nerve terminals. If the third-order postganglionic neuron is damaged (e.g., from carotid dissection or cluster headache), there are no functional terminals and no NE to release, so the pupil fails to dilate. An intact third-order neuron (first or second order lesion) would allow normal dilation.

A technician performs the swinging flashlight test and notices that when light is directed into the left eye, BOTH pupils constrict briskly, but when light swings to the right eye, both pupils dilate slightly before reconstricting. This pattern is most consistent with:

Answer: A right relative afferent pupillary defect

In a right RAPD, the right optic nerve transmits a weaker light signal. When light shines into the right eye, both pupils perceive a dimmer stimulus (compared to when light was in the left), causing consensual and direct dilation. The dilation occurs in BOTH pupils simultaneously because the efferent pathway is intact — this confirms the defect is afferent (right optic nerve), not efferent.

Dilute pilocarpine 0.1% is instilled in both eyes of a patient with a unilaterally large, poorly reactive pupil. The affected pupil constricts noticeably while the fellow pupil shows no response. What condition does this confirm?

Answer: Adie's tonic pupil with postganglionic denervation supersensitivity

Postganglionic denervation (as in Adie's tonic pupil) causes upregulation of muscarinic receptors at the iris sphincter. This supersensitivity allows a sub-pharmacological dose (0.1% pilocarpine) to constrict the affected eye while having no effect on the normal fellow eye. A pharmacologically blocked pupil (atropine) would NOT constrict even with 1% pilocarpine, because the receptors are occupied.

A patient presents with bilaterally small, irregular pupils that constrict briskly to a near target but show minimal reaction to a bright light. Slit-lamp examination reveals no posterior synechiae. Which additional finding would most strongly support the classic diagnosis?

Answer: Positive FTA-ABS serology

The described pupils — small, irregular, near-light dissociated, without synechiae — are classic Argyll Robertson pupils, historically pathognomonic for neurosyphilis. The FTA-ABS (fluorescent treponemal antibody absorption) test is the gold standard confirmatory serology. The light-near dissociation results from a dorsal midbrain lesion that disrupts the pretectal light-reflex pathway while sparing the more ventral near-reflex pathway.

A patient arrives with a unilaterally dilated, non-reactive pupil following a workplace chemical splash. To differentiate pharmacological mydriasis from a ruptured posterior communicating artery aneurysm compressing CN III, the technician should instill:

Answer: Pilocarpine 1%, which will constrict the CN III-palsy pupil but not the pharmacologically dilated pupil

Pharmacological mydriasis (e.g., from atropine or tropicamide splash) competitively blocks muscarinic receptors. Even 1% pilocarpine cannot overcome this blockade, so the pupil remains dilated. In CN III palsy, the iris sphincter muscle and its muscarinic receptors are structurally intact — only the nerve input is absent — so 1% pilocarpine directly stimulates the receptors and causes constriction. This distinction is critical: a CN III palsy from aneurysm is a neurosurgical emergency.