Dark-adapted luminance-response functions with skin and corneal electrodes

Abstract

Normative dark-adapted electroretinograms were recorded simultaneously with a skin electrode and corneal electrode for varying stimulus intensities. The electroretinogram b-wave amplitudes for each electrode were fitted by the Naka-Rushton equation, and the parameters Vmax, K and n were evaluated. A comparison of parameters between the two electrodes showed a significant difference for Vmax and K but not for n. Vmax was approximately eight times smaller and K was 0.3 log unit smaller for the skin electrode than for the corneal electrode. B-wave amplitude and implicit time were also compared between the two electrodes. The b-wave amplitude ratio of the corneal electrode to that of the skin electrode increased with luminance and ranged from 1.83 to 7.68. Overall, b-wave implicit time for the skin electrode was approximately 10 ms shorter than that of the corneal electrode.

The relationship between stimulus intensity and response amplitude for the photopic negative response of the flash electroretinogram

“…In our results, Vmax was significantly less variable than K in terms of intersubject CoV and also, in some cases, for inter-ocular and inter-session LoA. Wali and Leguire also found K to be the most variable parameter for the intensity-response series of the scotopic b-wave [43]. In a previous paper, we reported the variability of PhNR amplitudes measured in different ways in response to a stimulus of intensity 1.76 log phot td.s [21].…”

“…Bradshaw et al, (2004) also found that, when scaled for amplitude, the b-wave intensity-response series of the skin and corneal electrodes were similar [47]. In contrast, Wali and Leguire (1991) found skin electrode responses to have a lower K value than corneal electrode responses [43], indicating a greater sensitivity of the responses recorded using the skin electrode. However they were analysing scotopic b-wave amplitudes, rather than photopic ERGS.…”

“…These factors indicate that the DTL electrode is more suitable for clinically assessing the intensity-response series of the PhNR. Wali and Leguire (1991) compared the parameters of the dark adapted b-wave intensity-response function recorded using skin and corneal (jet contact lens) electrodes [43] and also reported that Vmax was more variable for the skin electrode, although they found the variability of K to be similar between electrode types.…”

Fundus pigmentation and the dark-adapted electroretinogram

“…Dark-adapted ERG amplitudes over a range of stimulus intensities constitute the luminance-response (L-R) function, which can be fitted by the Naka-Rushton equation [1]: V= (Vmax In)/(I n + Kn), with the use of nonlinear [2][3][4][5] or linear [6][7] regression. V is the measured b-wave amplitude at luminance I, Vmax is the maximum b-wave amplitude obtained, K is the half saturation constant (i.e., the luminance at which V = 89 Vmax) and n is a dimensionless constant that represents the slope of the function.…”

Full-field electroretinogram recorded with skin electrodes in normal adults

“…Previous studies with skin electrodes have demonstrated that peak-to-peak amplitude can show variability as the skin electrode can move during the exam, reducing the amplitudes on the final steps as the electrodes lose adherence to the skin (11) . However, comparative studies demonstrated that the variability found with skin electrodes is similar to the variability found with corneal contact electrodes, and examiners need to ensure that the electrode is correctly placed close to the lower orbital rim during the entire exam (9,22) . The ISCEV protocol and the recommendation for each laboratory to determine its own normative values are extremely important for a high quality test.…”