The Pupils

Normal light reflex pathway



  • 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)





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





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