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Multi-centre variability of ISCEV standard ERGs in two normal adults

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Abstract

Background

The reproducibility of an individual’s full-field ERG between centres has not previously been investigated.

Methods

ERGs were recorded using both silver thread and skin electrodes from the same two normal adult subjects at 15 UK centres using routine, local protocols and a highly standardised, ‘ISCEV-specified’ protocol matching the values specified in the ISCEV standard; where the ISCEV standard allows options, a single value was chosen.

Results

Inter-ocular differences were small, and amplitudes were smaller for skin than silver thread electrodes. No centre produced outlying data points, and ERGs across all 15 centres were remarkably similar. Amplitude variability was less for local protocols (using LED flashes) than for the ISCEV-specified protocol using xenon flashes (22 vs. 24 %, p = 0.01), but peak time variability was less for the ISCEV-specified protocol (6.1 vs. 7.4 %, p = 0.001). Only the DA 0.01 ERG correlated with photometric variability. The bifidity of the DA 3 a-wave doubled its peak time variability compared with the DA 10 a-wave.

Conclusions

Inter-centre amplitude variability was typically within clinically significant thresholds, suggesting that inter-centre variability with suitable standardisation may not add more to total variability than inter-subject variability. Variability improvements gained by the tighter specifications of the ISCEV-specified protocol were possibly more than lost due to imprecisions of xenon flashtubes. Peak time variability was far lower than amplitude variability, corresponding with acceptable variability of biochemical assays. These results represent a vindication of the existence of an ERG standard and suggest that further standardisation would lend itself to greater reproducibility of ERGs worldwide.

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Notes

  1. Photopic specification assumed hereafter for photometric units.

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Acknowledgments

We gratefully acknowledge the following: Mrs. Mary Broadberry, Dr. Paul Spry, Professor Daphne McCulloch, Dr. Richard Hagan, Dr. Neil Parry, Mr. Chris Hogg, Mrs. Karen Bradshaw, Mrs. Beverley Holland, Dr. Charles Cottrial and Dr. Gillian Ruddock; Mr Donnie Smith, Medical Device Section, Department of Clinical Physics and Bioengineering, NHS Greater Glasgow & Clyde, UK, for design and manufacture of the amplifier calibrator. These data were presented at ISCEV 2012 and BriSCEV 2012.

Conflict of interest

The authors accepted a donation of the silver thread electrodes used from Professor Anthony Fisher, Department of Clinical Engineering, Royal Broadgreen Liverpool Hospitals. All authors are, or have been, members of ISCEV, which has non-financial interest in the ERG standard discussed in this manuscript and which awarded a small grant for laboratory visits to part-fund the project. All authors certify that they have no other affiliation with or involvement in any organisation or entity with any financial or non-financial interest in the subject matter or materials discussed in this manuscript.

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Authors and Affiliations

  1. Department of Clinical Physics, Royal Hospital for Sick Children, NHS Greater Glasgow and Clyde, University of Glasgow, Dalnair Street, Glasgow, G3 8SJ, UK

    R. Hamilton & D. Keating

  2. Vision Sciences, Glasgow Caledonian University, Glasgow, UK

    A. Al Abdlseaed

  3. Clinical Engineering, Sheffield Teaching Hospitals NHS Foundation Trust, Sheffield, UK

    J. Healey & L. Brown

  4. Electrophysiology Department, Moorfields Eye Hospital, London, UK

    M. M. Neveu

  5. Eye Department, Aberdeen Royal Infirmary, Foresterhill, UK

    V. A. McBain

  6. Eye Department, Stoke Mandeville Hospital, Aylesbury, UK

    D. Sculfor

  7. Clinical and Academic Department of Ophthalmology, Great Ormond Street Hospital for Children NHS Foundation Trust, London, UK

    D. A. Thompson

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  1. R. Hamilton
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Correspondence to R. Hamilton.

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Hamilton, R., Al Abdlseaed, A., Healey, J. et al. Multi-centre variability of ISCEV standard ERGs in two normal adults. Doc Ophthalmol 130, 83–101 (2015). https://doi.org/10.1007/s10633-014-9471-9

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  • DOI: https://doi.org/10.1007/s10633-014-9471-9

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