The Pupils

Normal light reflex pathway

Hippus

• In steady illumination, normal pupil is continuously dilating and contracting. This is called hippus (pupil undulation).

Simple anicosoria

• Definition of anicosoria: >0.5mm different in dize of the left and right pupil
• Simple = cannot be atributed to secondary causes eg trauma, drugs etc, occurs in up to 40% of healthy persons

Normal light reflex

• Direct and consensual reaction
  – Direct: ipsilateral pupillary constriction
  – Consensual: contralateral pupillary constriction
• Clinical significance: Anicosoria is
  – absent in disorders of the optic nerve or retina (i.e afferent connections)
  – present in asymmetric disease of the iris, sympathetic nerve or oculomotor nerve
     (i.e efferent connections)

Near synkinesis reaction: when a person focuses on near object:

• Constriction
• Convergence
• Accomodation

Abnormal pupils

• RAPD (Marcus-Gunn pupil)
• Argyll Robertson pupils
• Oval (dilated pupils)
• Anicosoria

Relative afferent pupil defect (Marcus-Gunn pupil)

• Detected by swinging flashlight test
• Finding: detection of absence of direct or consensual response of the pupil
• Clinical significance:
  – Optic nerve disease (eg optic neuritis, ischemic optic neuropathy)
  ** Cataracts DO NOT cause RAPD as the retina behind it is intact.

Argyll-Robertson pupils

• Mnemonic: ARP PRA
  – Accomodation reflex present, pupillary reflex absent
  – Bilateral SMALL PUPILS
  – Constriction & redilation of pupils are brisk
• Historically due to 3rd stage of syphilis
• Differential diagnosis of light-near dissociation
  – Adie’s tonic pupil
  – Parinaud syndrome (dorsal midbrain syndrome)
  – Aberrant regeneration of third nerve
• Parinaud syndrome (dorsal midbrain syndrome)
  – Ddx: young: pinealoma; middle age lady: MS; old: basilar artery stroke
  – CLUES: Convergence-retraction nystagmus, Light near dissociation, Upward deviation, Eyelid retraction, Setting sun sign

Oval pupil

• Third nerve palsy from brain herniation
• Adie’s tonic pupil
• Previus surgery or trauma to iris (pupillary constrictor)

Pathological anicosoria

• Which side is abnormal?
  – Swing a flashlight to the dilated eye. If the ipsilateral eye does not constrict, the pupillary constrictor at the side is abnormal. If it does constrict, the contralateral (smaller) eye is abnormal.
• 2 questions
  i) Is there full 3rd nerve palsy?
  ii) Neurological findings?

Smaller eye is the problem:

• Horner syndrome
• Simple anicosoria

Bigger eye is the problem:

• 3rd nerve palsy from brain herniation or Hutchinson pupil (if comatose) or PCA aneurysm (if not comatose)
  – Ptosis and pupil will appear “down and out” in 3rd nerve compression
• Adie’s tonic pupil (respond to pilocarpine)
• Anticholinergic mydriasis (does not respond to pilocarpine)

Adie’s tonic pupil

• Unilateral LARGE PUPIL
• Tonic = SLOW constriction and redilation in respponse to near vision
• Light reflex is absent
• Adie’s syndrome: tonic pupil + hyperhidrosis + areflexia
• Due to injury to the ciliary ganglion and postganglionic fibers (eg viral infection)
  – The fibers destined to ciliary body instead aberrantly re-innervate pupillary constrictor. Hence, the loss of light reflex.

Horner syndrome

• Ptosis, miosis, anhidrosis, enophthalmos
• Presence or absence of anhidrosis may indicate level of lesion
  – 1st order (preganglionic eg stroke): anhidrosis present in face and trunk
  – 2nd order (ganglionic eg Pancoast syndrome, cervical rib): anhidrosis only in face
  – 3rd order (postganglionic eg ICA dissection): no facial anhidrosis 
  – This is because neurons to facial sweat glands are located in ECA
  – However, this was found to be limited in utility (not significant LR)

Summary

Reference:

Steven McGee. Evidence based Physical Diagnosis. Pg 209-233