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. 2001 Apr;85(4):403–409. doi: 10.1136/bjo.85.4.403

The b-wave of the dark adapted flash electroretinogram in patients with advanced asymmetrical glaucoma and normal subjects

I Velten 1, F Horn 1, M Korth 1, K Velten 1
PMCID: PMC1723928  PMID: 11264127

Abstract

AIMS—To evaluate whether the b-wave of the dark adapted flash electroretinogram (ERG) is affected by glaucomatous damage.
METHODS—ERGs were recorded in 35 patients aged 33-65 years with advanced asymmetrical glaucomas (interocular difference of perimetric defects (mean deviation) >2 dB between the two fellow eyes of the glaucoma patients, primary and secondary open angle and low tension glaucomas) and 17 normal subjects matched for age and sex using white flashes of a xenon discharge tube in a Ganzfeld stimulator. After 30 minutes of dark adaptation luminance response functions were obtained using flashes of increasing scotopic luminance (highest 9.4 cd/s/m2, lowest 5.5 log units below it). The parameters Vmax, n, and K of the Naka-Rushton equation were computed from the measurement values based on the usual fitting procedure. These parameters, together with b-wave amplitudes and implicit times for all flash intensities, were compared interocularly and between the normal subjects and those with glaucoma. Correlations were computed between interocular differences of the mean deviation and interocular differences of Vmax, n, K, b-wave amplitudes, and implicit times between the two fellow eyes of the patients with asymmetrical glaucomatous damage.
RESULTS—Implicit times were significantly longer (p<0.005) in the glaucoma patients than in the normal group for flash intensities of 9.4, 5.3, 1.7, 0.53, and 0.17 cd/s/m2. b-Wave amplitudes did not differ significantly between the two study groups. Comparing the two fellow eyes of each patient with glaucoma, Vmax was significantly higher in the less damaged eye than in the more damaged eye. The interocular differences in the mean deviation correlated significantly with the interocular differences in the b-wave amplitudes, implicit times, and Vmax.
CONCLUSIONS—These results suggest that glaucomas can lead to electrophysiologically measurable damage of the inner nuclear layer.



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Figure 1  .

Figure 1  

Figure 1  

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(A) Comparison between the intensity response data and the first model of the Naka-Rushton function fitted to all data points. The patient suffered from asymmetrical juvenile open angle glaucoma of the left eye (mean deviation in right eye (RE) -1.0 dB, mean deviation in left eye (LE) 8.7 dB). The parameters of the Naka-Rushton equation are: Vmax = 395 µm, K = -3.02 log units, n = 0.65 for the right eye and Vmax = 351 µm, K = -3.19 log units, n = 0.63 for the left eye. (B) Intensity response data of the right and left eyes of the same patient. In contrast to (A), this figure demonstrates the second model of the Naka-Rushton equation with fit of the function to data points below -1.25 log units (0.53 cd/s/m2) and thus below the "second limb" of the intensity response function. The parameters of the second model of the Naka-Rushton equation are: Vmax = 298 µm, K = -3.36 log units, n = 1.55 for the right eye and Vmax = 288 µm, K = -3.47 log units, n = 1.06 for the left eye.    

Figure 2  .

Figure 2  

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Vmax2 of the more and less damaged fellow eyes of all glaucoma patients included in the interocular comparison (interocular difference in mean deviation >2 dB). In 18 of the 26 patients Vmax2 was higher in the fellow eye with the less advanced glaucomatous damage.

Selected References

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