Mapping of retinal function with the multi-input ERG by using a new technique. The scanning laser ophthalmoscope evoked multifocal-ERG (SLO-m-ERG).G. Rudolph1, T. Berninger1, G.B. Arden2, M. Bechmann1, I. Zolnikova3, C. Hörmann1, A. Kampik1
Purpose: Topographic mapping of retinal function in the central visual field by using a confocal scanning laser ophthalmoscope evoked multifocal electroretinogram (SLO-m-ERG). To demonstrate the possibility to analyze the linear approximation (first order kernel), the nonlinear approximation (second order kernel) and the second order response.
Methods: A confocal scanning laser ophthalmoscope is used as a stimulator and trigger unit to perform a multifocal-ERG. The stimulus matrix of 19-241 hexagonal elements is covering a visual field of 24° . The visual stimulus is generated by a helium-neon laser (632,8 nm) with a power range of 0-200 m W. Simultaneous funduscopy and control of fixation is given by using a infrared laser (780 nm) ivith a power range of 0-2000 m W. The posterior pole of the eye and the hexagonal matrix are visualized on a video screen. The frame rate is 50 Hz. To record the m- ERG a bipolar Jet-electrode, which allows clear observation of the fundus during the examination, is used. The software is able to analyze the linear approximation (first order kernel) as well as the nonlinear approximation (second order kernel) and the second order response. The software provides also the possibility to calculate the first order response from given amplitude densities of the second order component.
Results: Examinations in patients with impaired retinal function due to lesions on the posterior pole of the retina show reduction of amplitudes in the first and second order component. The amplitude density can be measured in any given hexagon. It is also possible to get averaged values of areas with the same eccentricity (rings) or of other subsets (quadrants or defined user groups). Results are obtained in patients with macular dystrophies, age related macular degeneration, macular holes, diabetes, glaucoma, inflammatory retinal disorders and retinal dysfunction without visible morphologic alterations. In comparison to the monitor stimulated m-ERG the latencies of the a- and b-wave are significantly longer by using the SLO-m-ERG technique.
Conclusion: The scanning laser ophthalmoscope evoked m-ERG offers a new method of topographic mapping of retinal function under control of fixation. The technique creates the possibility to directly correlate an electrophysiological response to a certain area of the retina. The first order component seems to be helpfull to analyze the function of the outer retina, while the second order component, originating mainly or for a certain amount of the inner retina, may be of interest in evaluating retinal function in patients with glaucoma or diabetes mellitus. Since the examined test field covers only the central 24° the SLO-m-ERG is especially suitable to perform diagnostic in patients ivith retinal disorders of the posterior pole of the eye.
1Augenklinik der Ludwig-Maximilians-Universität, Mathildenstrasse 8, D-80336 München
2City University, Goswell Road 321, UK- EC1V7DD London
3Moscow Medical Setchenov Academy, Bolschaya Pirogovskaya 6-8. RF-119881 Moscow