Rare pupil anomalies (PT3)

Other Pupil Anomalies

• LIGHT-NEAR DISSOCIATION:

  • The afferent pathway for the pupil near reflex is different from the afferent pathway for the pupil light reflex.

  • Some patients may present with anomalous reactions to light but a normal near response.

  • Examples include Argyll Robertson pupils, Dorsal mid-brain syndrome, and amaurotic pupils.

Argyll Robertson Pupils

• Bilateral, irregular, miotic pupils (small pupils) where the light reflex is absent, but the near reflex is preserved.

  • In dim light, both pupils are small and may be irregular.

  • In bright light, neither pupil constricts, but on accommodation (focusing on a near target), both constrict.

  • Cause: A midbrain lesion that interrupts the pupillary light reflex pathway but spares the more ventral pupillary near reflex pathway.

    • Commonly caused by neurosyphilis.

    • Other possible causes include diabetes and alcoholism.

A - dim illumination, B - bright illumination, C - near work

• Characteristics:

  • Absent light reaction.

  • Small pupils in ambient light.

  • Brisk reaction preserved to accommodation.

Dorsal Midbrain Syndrome

• Light-Near Dissociation occurs when afferent pupil fibers are affected in the midbrain (pretectal) area.

  • Light reaction may be diminished or lost, while the near reaction is maintained.

  • Pupils tend to be mid-sized or dilated and frequently unequal.

  • Normal near reflex but no light reflex bilaterally.

  • May be associated with impairment of upgaze due to damage of the vertical gaze center and convergence retraction nystagmus.

  • Causes:

    • Pineal tumor (pinealoma).

    • Hydrocephalus, meningitis.

    • Stroke or multiple sclerosis.

Amaurotic Pupils (Absolute Afferent Pupil Defect)

• Caused by a complete optic nerve lesion where the involved eye is completely blind (i.e., no light perception).

  • Both pupils are of equal size.

  • No light reaction occurs when the affected eye is stimulated.

  • Both pupils react normally when the contralateral normal eye is stimulated.

  • Reaction of both pupils to near is normal.

Benign Episodic Unilateral Mydriasis

• Uncommon cause of intermittent/transient anisocoria (unequal pupil sizes).

  • Isolated benign, idiopathic cause of pupil asymmetry.

  • Most common in young adult females.

  • Often associated with a migraine attack, or patients may have a history of past migraines.

  • May be due to:

    • Parasympathetic insufficiency.

    • Sympathetic hyperactivity.

Parasympathetic Form:

• Pupil enlarged and poorly reactive.

  • Poor reaction of dilated pupil to light and near stimuli.

  • Reduced accommodation.

  • No ocular motor dysfunction or ptosis.

  • Duration is typically 15 minutes to several hours.

Sympathetic Form:

• Pupil transiently enlarged.

  • Pupil may be distorted (tadpole pupil) due to a segmental spasm of the iris dilator.

  • Brisk reaction to light, normal accommodation.

  • Often asymptomatic.

  • Possibly blurred vision, increased light sensitivity.

  • Duration is typically 15 minutes to several hours.