June 2006
Volume 6, Issue 6
Free
Vision Sciences Society Annual Meeting Abstract  |   June 2006
Second sight: Vision sustained by a secondary activation of the phototransduction cascade
Author Affiliations
  • Andrew Stockman
    Institute of Ophthalmology, University College London, 11-43 Bath Street, London EC1V 9EL, UK
  • Lindsay T. Sharpe
    Institute of Ophthalmology, University College London, 11-43 Bath Street, London EC1V 9EL, UK
  • Michel Michaelides
    Institute of Ophthalmology, University College London, 11-43 Bath Street, London EC1V 9EL, UK, and Moorfields Eye Hospital, 162 City Road, London EC1V 2PD, UK
  • Anthony T. Moore
    Institute of Ophthalmology, University College London, 11-43 Bath Street, London EC1V 9EL, UK, and Moorfields Eye Hospital, 162 City Road, London EC1V 2PD, UK
  • Andrew R. Webster
    Institute of Ophthalmology, University College London, 11-43 Bath Street, London EC1V 9EL, UK, and Moorfields Eye Hospital, 162 City Road, London EC1V 2PD, UK
  • Hannah E. Smithson
    Institute of Ophthalmology, University College London, 11-43 Bath Street, London EC1V 9EL, UK, and Department of Experimental Psychology, University of Durham, South Road, Durham, DH13EL, UK
Journal of Vision June 2006, Vol.6, 120. doi:10.1167/6.6.120
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      Andrew Stockman, Lindsay T. Sharpe, Michel Michaelides, Anthony T. Moore, Andrew R. Webster, Hannah E. Smithson; Second sight: Vision sustained by a secondary activation of the phototransduction cascade. Journal of Vision 2006;6(6):120. doi: 10.1167/6.6.120.

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

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Abstract

Introduction: A father and son are homozygous for a rare frameshift mutation (M280fsX291) in the gene encoding the a-subunit of cone transducin (GNAT2), the G-protein in the cone phototransduction cascade. Although this mutation should entirely abolish their cone vision, it does not. Here, we investigate the properties of their residual cone vision.

Methods: We measured cone-mediated critical-flicker-fusion as a function of the radiance of a 650 nm red target, and temporal modulation sensitivity as a function of temporal frequency at a fixed time-averaged 650 nm radiance (of 10.68 log quanta s−1 deg−2). Targets were superimposed in the centre of a 480 nm, rod-saturating background. Additional spectral sensitivity and bleaching controls were carried out to ensure that the responses were cone responses.

Results: Both father and son retain a rudimentary cone-driven response restricted to high light levels and low temporal frequencies, which has two singular properties. First, temporal frequency sensitivity is limited by the equivalent of a simple 1st order reaction with a time constant of ∼140 ms. Second, their temporal acuity is linearly related to the logarithm of the amount of bleached cone pigment.

Conclusion: The results are consistent with the residual cone response being dependent on the secondary activation of the phototransduction cascade by a bleaching photoproduct produced by a first-order reaction, such as a metarhodopsin derivative or the freed opsin, which bypasses the defective α-transducin. Such a secondary activation has long been hypothesized to explain the equivalence between the visual effects of bleaches and those of steady background lights.

Stockman, A. Sharpe, L. T. Michaelides, M. Moore, A. T. Webster, A. R. Smithson, H. E. (2006). Second sight: Vision sustained by a secondary activation of the phototransduction cascade [Abstract]. Journal of Vision, 6(6):120, 120a, http://journalofvision.org/6/6/120/, doi:10.1167/6.6.120. [CrossRef]
Footnotes
 Wellcome Trust
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