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

Aims-To evaluate whether the b-wave of the dark adapted flash electroretino gram (ERG) is affected by glaucomatous damage. Methods-ERGs were recorded in 35 patients aged 33-65 years with advanced as ymmetrical glaucomas (interocular difference of perimetric defects (mean de viation) >2 dB between the two fellow eyes of the glaucoma patients, primar y and secondary open angle and low tension glaucomas) and 17 normal subject s matched for age and sex using white hashes of a xenon discharge tube in a Ganzfeld stimulator. After 30 minutes of dark adaptation luminance respons e functions were obtained using flashes of increasing scotopic luminance (h ighest 9.4 cd/s/m(2), lowest 5.5 log units below it). The parameters V-max, n, and K of the Naka-Rushton equation were computed from the measurement v alues based on the usual fitting procedure. These parameters. together with b-wave amplitudes and implicit times for all flash intensities, were compa red interocularly and between the normal subjects and those with glaucoma. Correlations were computed between interocular differences of the mean devi ation and interocular differences of V-max, n, K, b-wave amplitudes, and im plicit times between the two fellow eyes of the patients with asymmetrical glaucomatous damage. Results-implicit times were significantly longer (p < 0.005) in the glaucom a patients than in the normal group for flash intensities of 9.4, 5.3, 1.7, 0.53, and 0.17 cd/s/m(2). b-Wave amplitudes did not differ significantly b etween the two study groups. Comparing the two fellow eyes of each patient with glaucoma, V-max 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 amp litudes, implicit times, and V-max. Conclusions-These results suggest that glaucomas can lead to electrophysiol ogically measurable damage of the inner nuclear layer.