December 2006
Volume 6, Issue 13
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OSA Fall Vision Meeting Abstract  |   December 2006
Transient tritanopia of a second kind redux: Delayed loss of S-cone sensitivity after long-wavelength field onset is consistent with the sluggish generation of an active photoproduct within the L- and M-cones
Author Affiliations
  • Andrew Stockman
    Institute of Ophthalmology, University College London, London, UK
  • Hannah E. Smithson
    Experimental Psychology, University of Durham
Journal of Vision December 2006, Vol.6, 5. doi:10.1167/6.13.5
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      Andrew Stockman, Hannah E. Smithson; Transient tritanopia of a second kind redux: Delayed loss of S-cone sensitivity after long-wavelength field onset is consistent with the sluggish generation of an active photoproduct within the L- and M-cones. Journal of Vision 2006;6(13):5. doi: 10.1167/6.13.5.

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Abstract

Mollon, Stockman & Polden (1987) reported an anomaly in the time-course of the light adaptation of the S-cone mechanism following the onset of an intense yellow bleaching light. Instead of recovering monotonically, S-cone increment threshold rises for several seconds before falling to its light-adapted steady-state value. As far as we aware, no mechanism has yet been proposed that provides a compelling explanation of this phenomenon.

As Mollon et al. showed, the anomaly must be mediated postreceptorally. We believe that the delayed suppression of S-cone sensitivity is not a property of the S-cone chromatic system per se, but instead reflects changes in the outputs of the L- and M-cones caused by the sluggish generation of an intermediate, active bleaching photoproduct within the L- and M-cone photoreceptors (some photoproducts are known to act much like real lights). We find that the time course of the rise and fall in S-cone threshold is consistent with the lifetime of an active photoproduct limited by two approximately first-order reactions with time constants of c. 5 and 20 s, which are likely to correspond to the rates of production and decay of the photoproduct. The S-cone thresholds are largely immune to the direct effects of photopigment depletion and other mechanisms of photoreceptor adaptation that affect the L- and M-cone thresholds (which recover monotonically). Consequently, this curious anomaly may provide a unique method of probing in vivo a part of the retinoid cycle that regenerates bleached photopigment in isolation from the usual photoreceptor adaptation mechanisms.

Stockman, A. Smithson, H. E. (2006). Transient tritanopia of a second kind redux: Delayed loss of S-cone sensitivity after long-wavelength field onset is consistent with the sluggish generation of an active photoproduct within the L- and M-cones [Abstract]. Journal of Vision, 6(13):5, 5a, http://journalofvision.org/6/13/5/, doi:10.1167/6.13.5. [CrossRef]
Footnotes
 Supported by the Wellcome Trust and Fight for Sight
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