November 2012
Volume 53, Issue 12
Free
Letters to the Editor  |   November 2012
Pupil Dynamics and Response Amplitude: Only Size Matters
Author Notes
  • ARC Centre of Excellence in Vision Science, John Curtin School of Medical Research, Australian National University, Canberra, Australia. 
Investigative Ophthalmology & Visual Science November 2012, Vol.53, 7644. doi:10.1167/iovs.12-11105
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      Ted Maddess; Pupil Dynamics and Response Amplitude: Only Size Matters. Invest. Ophthalmol. Vis. Sci. 2012;53(12):7644. doi: 10.1167/iovs.12-11105.

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      © ARVO (1962-2015); The Authors (2016-present)

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Bremner 1 provides an excellent demonstration in 43 healthy subjects that peak pupillary constriction velocity scales with the peak amplitude of constriction. This relationship is shown to be maintained over a wide range of stimulus intensities and does not depend on the age or natural pupil size of the subjects. Such a demonstration in a reasonably large population is valuable clinically and scientifically. It is worth noting that the relationship between pupil size and velocity was reported first by Semmlow and Stark, 2,3 albeit in a smaller number of subjects. Importantly they used phase plane analysis, in which the pupil velocity waveform is plotted against the waveform describing instantaneous pupil diameter. That analysis showed not only that the peak velocity scaled with amplitude, but that, indeed, the whole phase plane plot scaled isomorphically, that is every part of the pupillary response waveform scaled similarly. They also showed that, while waveforms for responses to changes in accommodation, fusional vergence, or light level had different dynamics, nevertheless all points on the evolving velocity waveforms scaled with instantaneous amplitude. Thus, they remarked that “all constriction movements have peak velocities and duration consistent with the movement amplitude, and the major response variation with mean pupil size is one of response amplitude alone.” In other words, amplitude scaled everything linearly in all the conditions they tested. These studies unfortunately were notmentioned in the new study and so they are mentioned here for the record. 
References
Bremner FD. Pupillometric evaluation of the dynamics of the pupillary response to a brief light stimulus in healthy subjects. Invest Ophthalmol Vis Sci . 2012;53:7343–7347. [CrossRef] [PubMed]
Semmlow J Stark L. Pupil movements to light and accommodative stimulation: a comparative study. Vision Res . 1973;13:1087–1100. [CrossRef] [PubMed]
Semmlow J Hansmann D Stark L. Variation in pupillomotor responsiveness with mean pupil size. Vision Res . 1975;15:85–90. [CrossRef] [PubMed]
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