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. 2001 Apr;85(4):397–402. doi: 10.1136/bjo.85.4.397

The a-wave of the dark adapted electroretinogram in glaucomas: are photoreceptors affected?

I Velten 1, M Korth 1, F Horn 1
PMCID: PMC1723933  PMID: 11264126

Abstract

AIMS—To evaluate whether the a-wave of the dark adapted flash electroretinogram (ERG) is affected by glaucomatous damage.
METHODS—ERGs were recorded in 20 patients (age 33-65 years) with advanced glaucomas (primary and secondary open angle and low tension glaucomas) and 20 normals using a ganzfeld stimulus. After 30 minutes of dark adaptation and pupil dilatation to at least 7.5 mm in diameter, luminance response functions were obtained presenting white flashes of increasing scotopic luminance (the highest flash intensity being 9.4 cd/s/m2, the lowest being 5.75 log units below it) with an interflash interval of 5 seconds. For each scotopic luminance, the responses of four flashes were averaged. The a-wave's amplitude was measured at 10, 11, and 12 ms. Within the glaucoma group, correlations between the interocular differences of the a-wave's amplitude and the mean deviation of a static perimetry (Octopus 500 perimeter, program G1) were computed for all flash intensities. Between normals and glaucomas, the a-wave's amplitude was compared for all flash intensities (paired t test).
RESULTS—Within the glaucoma group, the interocular differences of the a-wave's amplitudes correlated significantly with the differences of the MD for flash intensities of 9.4, 5.3, 1.7, and 0.5 cd/s/m2. The a-wave's amplitude was significantly lower in the glaucoma compared with the normal group (p <0.005) for flash intensities of 9.4 and 5.3 cd/s/m2.
CONCLUSION—These electrophysiological results imply that also the outer retinal structures, especially the photoreceptors, may be affected by glaucomatous damage.



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Figure 1  .

Figure 1  

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ERG responses of one normal subject for flash intensities of 0.2, 0.5, 1.7, 5.3, and 9.4 cd/s/m2. The broken line marks the time of 11 ms at which the response magnitudes were measured. This time was short enough to avoid interference of the a-wave with the b-wave.

Figure 2  .

Figure 2  

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(A-E) Scatter plots for the correlation between the interocular differences of the a-wave's amplitudes measured at a fixed time of 11 ms and the interocular differences of the MD between both fellow eyes of one patient within the glaucoma group for flash intensities of 9.4 cd/s/m2 (A), 5.3 cd/s/m2 (B), 1.7 cd/s/m2 (C, 0.5 cd/s/m2 (D), and 0.2 cd/s/m5 (E). Pearson's correlation was significant for luminance times of 9.4, 1.7, and 0.5 cd/s/m2 with correlation coefficients of 0.743, 0.660, 0.764, and 0.593, respectively (compare Table 2).

Figure 3  .

Figure 3  

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The a-wave's amplitudes measured at 11 ms for all subjects in the glaucoma and the normal group for flash intensities of 0.2, 0.5, 1.7, 5.3, and 9.4 cd/s/m2. For flash intensities of 9.4 and 5.3 cd/s/m2, the a-wave's amplitudes differed significantly between the two study groups (p <0.006, compare Table 2)

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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