Pupils

  • Measurement of size of pupils and their reactions to direct light stimulation
  • There are three steps:
    1. Detecting difference in pupil size ("anisocoria") in minimal illumination
    2. Measuring change in pupil size when exposed to bright light
    3. Detecting change in pupil size as bright light is swung back and forth between eyes, looking for a relative afferent pupil defect
  • Anisocoria may be physiologic if 1mm or less and both pupils constrict normally to direct light, but...
  • Anisocoria may also be sign of impaired neural transmission to iris sphincter or iris dilator
  • Impaired pupil constriction to direct light can signify impaired iris sphincter function, and...
  • Common causes of impaired iris sphincter function are eye surgery or trauma, tonic pupil, and third nerve palsy
  • Impaired iris dilator function is difficult to diagnose because it does not impair pupil constriction to direct light, so...
  • Instilling pharmacologic agents into eyes is necessary to confirm diagnosis of impaired iris dilator function, and...
  • Common cause of iris dilator dysfunction is Horner syndrome
  • Common cause of relative afferent pupil defect is optic neuropathy, but...
  • If you make technical mistakes in performing swinging light test, it will be unreliable!