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

Aims-To evaluate whether the a-wave of the dark adapted flash electroretino gram (ERG) is affected by glaucomatous damage. Methods-ERGs were recorded in 20 patients (age 33-65 years) with advanced g laucomas (primary and secondary open angle and low tension glaucomas) and 2 0 normals using a ganzfeld stimulus. After 30 minutes of dark adaptation an d pupil dilatation to at least 7.5 mm in diameter, luminance response funct ions were obtained presenting white flashes of increasing scotopic luminanc e (the highest flash intensity being 9.4 cd/s/m(2), the lowest being 5.75 l og units below it) with an interflash interval of 5 seconds. For each scoto pic luminance, the responses of four flashes were averaged. The a-wave's am plitude was measured at 10, 11, and 12 ms. Within the glaucoma group, corre lations between the interocular differences of the a-wave's amplitude and t he mean deviation of a static perimetry (Octopus 500 perimeter, program G1) were computed for all flash intensities. Between normals and glaucomas, th e a-wave's amplitude was compared for all flash intensities (paired t test) . Results-Within the glaucoma group, the interocular differences of the a-wav e'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/m(2). The a-wave's amplitu de 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/m(2). Conclusion-These electrophysiological results imply that also the outer ret inal structures, especially the photoreceptors, may be affected by glaucoma tous damage.