THE A-WAVE OF THE DARK-ADAPTED ELECTRORETINOGRAM IN GLAUCOMAS
I.M. Velten, M. Korth, F.K. Horn
Purpose: Histological studies of advanced glaucomatous eyes showed a reduced cell count not only of the retinal ganglion cells, but also of the outer retinal layers including the photoreceptors. The purpose of the study was to evaluate whether the a- wave of the flash-electroretinogram (as the response of the photoreceptors) is affected by glaucomatous damage.
Methods: Flash-ERGs were recorded in 20 patients (age 33 to 71 years) with advanced glaucomas (primary and secondary open-angle and low-tension glaucomas) and in 20 normals. White Flashes of a Xenon discharge tube in a ganzfeld were used. After 30 min of dark adaptation, flashes of increasing scotopic luminance (the highest being 5.3 cd s / m2, the lowest being 5.5 log units below it) were presented with an interflash interval of 5 sec. For each luminance, the responses of four flashes were averaged. The Naka-Rushton-equation was used to fit smooth curves to each luminance-response function of the a-waves peak amplitude. Its parameters Vmax, n, and k were compared interocularly and with a normal group matched for age (statistics: paired and unpaired t-test). Static perimetry with the Octopus 500 perimeter (program G 2 or G 3) was conducted in all patients in order to identify the more severely damaged eye. Patients were included if the difference of the mean defect (MD) was at least 1.5 dB between both eyes.
Results: In the glaucoma group, the maximum amplitude (Vmax), n, and k were significantly higher (p < 0.01) in the eye with the lower MD compared with the eye with the higher MD. Compared with the normal group, only Vmaxwas significantly lower in the glaucoma group (p < 0.05).
Conclusions: The lower maximum amplitude of the a-wave in the eye with the more advanced glaucoma damage and in the glaucoma compared with the normal group suggests that also the photoreceptors may be affected by glaucomatous damage.
(1) Panda S, Jonas JB: Decreased photoreceptor count in human eyes with secondary angle-closure glaucoma. Invest Ophthalmol Vis Sci, 1992; 33:2532-2536.
Supported by "Deutsche Forschungsgemeinschaft, Sonderforschungsbereich Glaukome (SFB 539) "
Augenklinik mit Polinik der Universität Erlangen-Nürnberg, Schwabachanlage 6, D-91054 Erlangen