Abstract
The photopic negative response (PhNR) has attracted interest as a flash ERG component reflecting inner retinal activity, with investigators adopting various approaches to analysing the response. This study has two principal aims: first to determine the most reliable technique for assessing the PhNR amplitude; secondly to compare the repeatability characteristics of the PhNR recorded using DTL and skin active electrodes. Electroretinograms were recorded in 31 subjects, using both electrode types, in response to a Ganzfeld red stimulus (Lee filter “bright red”; 1.76 log phot td.s; 4 Hz) presented over a steady blue background (Schott glass filter BG28; 3.9 log scot td). Sixteen subjects returned to assess repeatability. PhNR amplitude was measured from b-wave peak-to-PhNR trough, pre-stimulus baseline to trough, and from peak and baseline to a fixed time-point; a ratio of b-wave/PhNR amplitude was also calculated. Coefficients of variation (CoV), and inter-ocular and inter-session limits of agreement (LoA) were calculated for all measures. The ratio of b-wave/PhNR amplitude showed the lowest CoV (14.3% DTL; 23.2% skin), inter-ocular LoA (22.2% DTL; 25.0% skin), and inter-session LoA (22.8% DTL; 20.3% skin). The peak-to-trough and peak-to-fixed-time measurements were also consistently reliable. Least reliable measures were those measured from baseline. While skin electrode responses were significantly smaller than DTL responses (P < 0.0001), the variability was only slightly increased. This study suggests that peak-to-trough measurements are the most reliable means of measuring the PhNR and ratio calculation further improves repeatability. Skin electrodes provided a viable alternative to DTL electrodes for recording the PhNR.
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Abbreviations
- PT:
-
Peak-to-trough
- BT:
-
Baseline to trough
- BF:
-
Baseline to fixed time-point
- PF:
-
Peak-to-fixed time-point
- PTR:
-
Ratio b-wave / PhNR measured from peak-to-trough
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Acknowledgments
The UK & Eire Glaucoma Society, International Glaucoma Association, and the Wellcome Trust are acknowledged for funding of research that led to the publication of this paper. We would like to thank Mei Tan and Neelam Mohamed for their assistance in the collection of some of the data.
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Mortlock, K.E., Binns, A.M., Aldebasi, Y.H. et al. Inter-subject, inter-ocular and inter-session repeatability of the photopic negative response of the electroretinogram recorded using DTL and skin electrodes. Doc Ophthalmol 121, 123–134 (2010). https://doi.org/10.1007/s10633-010-9239-9
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DOI: https://doi.org/10.1007/s10633-010-9239-9