Detection of the pupil constriction latency

J. E. Bos*

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review


Two methods to accurately determine the moment of pupil constriction onset are discussed. For data sampled at a high rate (≈200 Hz) pupil velocity deviations from zero can simply be used, giving a satisfactory inaccuracy of about 5 ms. For data sampled at a low rate (<50 Hz), e.g. using a TV pupillometer, curve-fitting can be applied. It is demonstrated that curve-fitting, based on a second-order mathematical model, preceded by a linear trend, can result in an inaccuracy of less than 5 ms. Both methods give latencies independent of signal amplitude. This implies that a pupillometer yielding a relative measurement of the pupil area can be used for the detection of pupil constriction latencies. Furthermore it is demonstrated that the averaging of pupil constrictions results in an advanced moment of onset. Where latency differences of less than 25 ms are concerned, raw pupil data should therefore not be averaged.

Original languageEnglish
Pages (from-to)529-534
Number of pages6
JournalMedical & Biological Engineering & Computing
Issue number5
Publication statusPublished - 1 Sept 1991


  • Constriction
  • Latency
  • Light reaction
  • Pupil


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