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

Abstract

Glaucomas are known to lead primarily to damage of the retinal ganglion cell layer. Whether other inner, middle, and outer retinal structures can also be involved in glaucomatous changes has been the object of interest of many studies during the last years. Among others, glaucoma induced histological horizontal cell alterations in the human retina, 1 increased glutamine uptake, 2 and increased expression of glial fibrillary acidic protein 3 in Müller cells were found. Histological studies to determine whether glaucomatous damage also leads to damage of the outer retinal layers, especially the photoreceptors, have given controversial results.4 5 A number of electrophysiological studies have been performed [6][7][8][9] to establish whether the a-waves and b-waves of the flash electroretinogram (ERG) are aVected by glaucomatous damage. While some of these studies could not find any significant change in ERG responses related to glaucomas, 6 7 others 8 9 found significant changes in either the a-waves or the b-wave. The b-wave of the dark adapted flash ERG arises primarily from the on-bipolar cells, partially from the Müller cells. 10 11 It can therefore be regarded as a measure of the function of the middle retina, especially of the inner nuclear layer.In contrast to previous investigations, the present study examines the b-wave of the dark adapted ERG using a light intensity function. The peak amplitude of the b-wave was followed from its threshold up to high intensities lying above the intensity of the ISCEV standard 12 bright flash. Each individual intensity response function was modelled by the Naka-Rushton equation 13 and its three parameters (V max , n, and K) were obtained. Normal subjects show high interindividual variability in ERG responses. To reduce this variability an interocular comparison between the eye with the more advanced glaucoma damage and the less damaged fellow eye was used additionally in the comparison between the glaucomatous subjects and the normal group. This intraindividual interocular comparison enables a better determination of whether a relation exists between the stage of glaucoma damage and the impairment of the b-wave. It was thus the purpose of this study to determine electrophysiologically whether or not the middle retinal layers are included in advanced glaucomatous damage. To answer this question the study only used patients with long standing, advanced glaucomas with proven perimetric defects. Br J Ophthalmol 2001;85:403-409 403

Improved retinal function after trabeculectomy in glaucoma patients

“…We also compared the full-field ERG parameters of glaucoma patients with 25 healthy control subjects, and found significant differences in a-and b-waves implicit times and b-waves amplitudes, consistent with the findings discussed above [29,[43][44][45]. Thus, both the present and previous full-field ERG studies confirm a reduction in the retinal function in patients with glaucoma compared with controls.…”

“…Leydhecker reported normal values even from blind eyes (he defined blind eyes as eyes in which the visual acuity Table 4 Multifocal electroretinogram recordings from area 1 (macular retina) and area 2 (perimacular retina/periphery) in patients, preoperatively and 2 and 6 months postoperatively (n=11) and age-matched controls (n=11) was reduced to counting fingers, hand movements and perception of light) [42]. Since then, several investigators have evaluated glaucoma patients using full-field ERG, with conflicting results [29,[42][43][44][45]. As opposed to Leydhecker [42], Fazio et al [29] reported significant differences between control groups and glaucoma patients in several of the full-field ERG parameters, such as photopic a-wave and scotopic b-wave implicit times, dark-adapted bright flash awave amplitudes, and a-and b-wave implicit times.…”

“…Their findings were consistent with those of Fazio et al [29], although the changes in the flash ERG parameters in glaucoma patients were significantly larger than those in patients with optic atrophy. Velten et al [44,45] examined patients with advanced glaucoma using full-field ERG with a light intensity function. Their ERG results demonstrated that glaucoma may affect both the inner and outer retinal layer.…”

Transsynaptic Retinal Degeneration in Optic Neuropathies: Optical Coherence Tomography Study

“…In fact, functional impediment of INL has been reported in both conditions. 7,[31][32][33] Finally, changes in cellular composition of the overlying retinal layers (extensive loss of RNFL and ganglion cells) can potentially alter light reflectivity of INL structures and therefore influence the measurement of INL thickness. Our study is also limited by relatively small sample size and cross-sectional study design.…”

A hypothesis to explain ganglion cell death caused by vascular insults at the optic nerve head: possible implication for the treatment of glaucoma.

“…It is generally believed that the flash electroretinograms, and specifically the b-wave amplitude, from glaucoma patients are unaVected, which is consistent with this idea. It is worthy to note, however, that recent reports have shown a reduction of a-wave amplitude 82 and a delay in b-wave implicit times 83 in the dark adapted flash electroretinograms (ERGs) from patients with advanced glaucoma. Interestingly, the b-wave amplitude of the ERG is slightly reduced with ageing 84 and glaucoma has been described as an "ageing disease."…”