At the time of patient referral, the amount of glaucomatous optic nerve damage correlated significantly with a thin central cornea. Progression of glaucomatous optic nerve neuropathy was independent of central corneal thickness, suggesting that central corneal thickness may not play a major role in the pathogenesis of progressive glaucomatous optic nerve damage.

Aims-To evaluate whether the a-wave of the dark adapted flash electroretinogram (ERG) is aVected 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/m 2 , 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 diVerences 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). regarding the question whether glaucomatous damage also leads to damage of the outer retinal layers, especially the photoreceptors, or whether the glaucomatous damage remains strictly limited to the inner retinal layers. A number of electrophysiological studies [3][4][5][6] have been performed to answer the question whether the a-wave and b-wave of the flash electroretinogram (ERG) are aVected by glaucomatous damage. While some of these studies 3 4 could not find any significant change in ERG responses related to glaucomas, others 5 6 found significant changes in either the a-wave or the b-wave in glaucomas. Results-WithinThe a-wave of the dark adapted ERG arising mainly from the rods, 7 8 can be regarded as a suitable measure of the photoreceptor function. In contrast with previous investigations, the present study examined the a-wave of the dark adapted ERG using a light intensity function. The a-wave's amplitude was followed from its threshold up to high intensities lying above the intensity of the ISCEV standard 9 bright flash. The peak amplitude of the a-wave has long been recognised as being contaminated by the intrusion of the b-wave. This may be of varying influence depending on the stimulus conditions and the nature of the process aVecting retinal sensitivity. 7 We thus used as a measure of photoreceptor function in this study the a-wave's amplitude measured at fixed times of 10, 11, and 12 ms, before interference with the b-wave can occur. Normals show a high interindividual variability in ERG responses. Thus, in this study, additionally to the comparison between the normal and glaucoma group, the interocular diVerences of the a-wave's amplitude were correlated with the interocular diVerences of the mean deviation (MD) of a static perimetry. Neglecting the interindividual variability, this intraindividual interocular comparison allows a better answer to the question of whether a relation exists between the stage of gla...

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

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Only patients with ocular hypertension showed a significant difference in CCT compared with normals. Pachymetry thus should be conducted in those patients to avoid overestimation of the IOP by applanation tonometry. In most of the patients with low-tension and open-angle glaucomas however, CCT regarded without other parameters (e.g. corneal or scleral rigidity) plays a minor role in detection of elevated IOP according to the results of this study.