April 2010
Volume 51, Issue 13
ARVO Annual Meeting Abstract  |   April 2010
Photopic Hill Revisited
Author Affiliations & Notes
  • S. Dewhirst
    Faculty of Medicine, University of Ottawa, Ottawa, Ontario, Canada
  • A. Fournier
    Ophthalmology, Children's Hospital of Eastern Ontario, Ottawa, Ontario, Canada
  • B. C. Leonard
    University of Ottawa Eye Institute, Ottawa, Ontario, Canada
  • B. Hurley
    University of Ottawa Eye Institute, Ottawa, Ontario, Canada
  • S. G. Coupland
    University of Ottawa Eye Institute, Ottawa, Ontario, Canada
  • Footnotes
    Commercial Relationships  S. Dewhirst, None; A. Fournier, None; B.C. Leonard, None; B. Hurley, None; S.G. Coupland, None.
  • Footnotes
    Support  None.
Investigative Ophthalmology & Visual Science April 2010, Vol.51, 1501. doi:
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      S. Dewhirst, A. Fournier, B. C. Leonard, B. Hurley, S. G. Coupland; Photopic Hill Revisited. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1501.

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

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Purpose: : The photopic ERG has a luminance-response curve which shows b-wave amplitudes increasing to a maximum, and then decreasing to reach a non-zero plateau. This asymptotic luminance-response function has been referred to as the "Photopic Hill". The Photopic hill has been shown in primates to result from luminance dependent interaction of cone on- and off-responses. Recently, the Photopic hill has been modeled by the sum of a Gaussian function and a logistic growth function using a 16 step protocol (Hamilton et al. 2007) and has been tested in a small number (n=7) of patients. Herein we describe a photopic hill protocol using fewer steps which yields results that fit a combined Gaussian-logistic model and which are in good agreement with results previously obtained by Hamilton et al.

Methods: : Thus far Photopic hills have been obtained from 9 eyes of 6 normal subjects with dilated pupils using DTL fiber electrodes and an Espion e2 system (Diagnosys LLC), with background: 30 cd.m-2; flash stimuli: -1.2 to 3.0 log cd.sec.m-2 in eight steps. Two artifact-free ERGs were averaged at each step and b-wave amplitude values were fitted using a non-linear regression analysis (SigmaPlot v11.0).

Results: : Photopic hills were obtained from all subjects within 5-8 minutes. The mean Gaussian component amplitude Vgmax was 125.3 µV with a 95% confidence interval =(85.28, 155.36) and the mean Logistic component amplitude Vbmax was 62.7 µV with a 95% confidence interval =(36.75, 88.79). Using a 1:1.7 ratio of Burian-Allen:DTL amplitude ratio we found clear comparison with the Hamilton et al. model’s Vgmax and Vbmax parameters.

Conclusions: : The human Photopic hill is well described by a combined Gaussian and logistic growth function. We have developed a brief protocol taking 5 minutes which can be used to generate a combined Gaussian-logistic function that compares favorably with the Hamilton et al. model in normal subjects. Clinical utility of this protocol is under investigation.

Keywords: electroretinography: clinical • retina 

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