AIMSTo evaluate whether the b-wave of the dark adapted flash electroretinogram (ERG) is affected by glaucomatous damage.
METHODSERGs 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 V_max, 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 V_max, n, K, b-wave amplitudes, and implicit times between the two fellow eyes of the patients with asymmetrical glaucomatous damage.
RESULTSImplicit 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, 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 amplitudes, implicit times, and V_max.
CONCLUSIONSThese results suggest that glaucomas can lead to electrophysiologically measurable damage of the inner nuclear layer.