Pupillary Disorders

Pupil Anatomy & Physiology - Eye's Aperture Show

• Pupil: Central iris aperture; controls retinal light entry.
• Iris Muscles:
  • Sphincter Pupillae: Circular fibers.
    • Action: Miosis (constriction).
    • Innervation: Parasympathetic (CN III, Edinger-Westphal nucleus → ciliary ganglion).
  • Dilator Pupillae: Radial fibers.
    • Action: Mydriasis (dilation).
    • Innervation: Sympathetic (T1 → superior cervical ganglion).
• Size: Normal: 2-4 mm (light), 4-8 mm (dark).
• Anisocoria: Unequal pupils; physiological if < 1 mm difference.

⭐ The Edinger-Westphal nucleus provides preganglionic parasympathetic fibers for pupillary constriction via the ciliary ganglion.

Pupillary Reflexes - Pupil's Quick Dance

• Light Reflex: Pupil constricts in response to light.
  • Afferent: CN II (Optic N.)
  • Efferent: CN III (Oculomotor N. - Parasympathetic via Edinger-Westphal nucleus)
  • Direct (same eye) & Consensual (opposite eye) response.
• Near Reflex Triad: For focusing on near objects.
  • Accommodation (ciliary muscle contraction → lens thickens)
  • Convergence (eyes move inwards)
  • Miosis (pupil constriction)

⭐ Relative Afferent Pupillary Defect (RAPD) / Marcus Gunn Pupil: Detected by swinging flashlight test; affected pupil dilates paradoxically or constricts less when light swings from normal to affected eye. Indicates optic nerve disease.

Afferent Pupillary Defect - Gunn's Flashy Clue

• A.k.a. Marcus Gunn Pupil (MGP) / Relative Afferent Pupillary Defect (RAPD).
• Indicates unilateral or asymmetric optic nerve (CN II) / severe retinal disease (pre-chiasmal).
• Mechanism: ↓ afferent input from affected eye → ↓ direct light reflex; consensual reflex intact.
• Swinging Flashlight Test:
  • Light on normal eye: both pupils constrict.
  • Swing to affected eye: affected pupil shows paradoxical dilation or reduced constriction.
• 📌 RAPD: Relative Afferent Pupil Defect.

⭐ RAPD implies the lesion is anterior to the optic chiasm.

Efferent Pupillary Defects - Nerve Wreck Revels

Efferent defects disrupt pupil motor pathways (parasympathetic/sympathetic). 📌 Mnemonic: Nerve, Wreck, Revels.

• CN III (Oculomotor) Palsy ("Nerve")

  • Parasympathetic fiber damage → mydriasis.
  • Features: Ptosis, "down & out" eye, dilated non-reactive pupil.
  • Compressive (e.g., PCOM aneurysm): Painful, pupil involved.
  • Microvascular (e.g., DM, HTN): Pupil often spared.

  ⭐ Painful CN III palsy + Mydriasis = Posterior Communicating Artery (PCOM) aneurysm until proven otherwise.

• Adie's Tonic Pupil ("Wreck")

  • Ciliary ganglion/short ciliary nerve lesion (often idiopathic/post-viral).
  • Features: Unilateral mydriasis, poor light reaction, light-near dissociation (better near constriction). Vermiform iris movements.
  • Test: Constriction with dilute pilocarpine (0.1% or 0.125%) due to denervation hypersensitivity.

• Horner's Syndrome ("Revels")

  • Sympathetic pathway disruption (oculosympathetic paresis).
  • Triad: Miosis (constricted pupil), mild ptosis (~2mm), anhidrosis (variable).
  • Tests:
    • Cocaine 4%: Fails to dilate Horner's pupil (confirms).
    • Apraclonidine 0.5% or 1%: Dilates Horner's pupil (reversal of anisocoria, confirms).

Specific Pupillary Syndromes - Peculiar Peepers Parade

• Adie's Tonic Pupil: Unilateral dilated pupil; light-near dissociation (LND). Young women, ↓ DTRs (Holmes-Adie).

  ⭐ Shows cholinergic supersensitivity: constricts to dilute (0.125%) pilocarpine.

• Argyll Robertson Pupil (ARP): Bilateral small, irregular pupils; LND. 📌 ARP: Accom. Reflex Present, Pupil. Reflex Absent. Strong neurosyphilis link.
• Marcus Gunn Pupil (RAPD): Optic nerve lesion. Affected eye dilates: swinging flashlight test.
• Hutchinson's Pupil: Unilateral fixed, dilated pupil; CN III compression (uncal herniation).

High‑Yield Points - ⚡ Biggest Takeaways

• Marcus Gunn Pupil (APD) indicates optic nerve disease; paradoxical dilation with swinging flashlight test.
• Argyll Robertson Pupil shows light-near dissociation (accommodates, no light reaction); classic for neurosyphilis.
• Adie's Tonic Pupil: Dilated pupil, poor light reaction, slow near response, often with absent deep tendon reflexes.
• Horner's Syndrome: Triad of miosis, ptosis, and anhidrosis due to sympathetic pathway lesion.
• Third Nerve Palsy: Mydriasis with ptosis and "down and out" gaze suggests compression (e.g., aneurysm).