Documenta Ophthalmologica 88: 65-75, 1994. @ 1994 KluwerAcademic Publishers. Printed in the Netherlands. Differences between pattern-evoked electroretinograms obtained by a scanning laser ophthalmoscope and by a mechanical mirror system FOLKERT HORN & MATTHIAS KORTH Klinische Forschergruppe 'Glaukome' (Na 55 / 6-1), Universiti~ts-AugenklinikErlangen, Erlangen, Germany Accepted 18 February 1994 Key words: Maxwellian view system, Pattern electroretinogram, Scanning laser ophthalmo- scope, Spatial tuning Abstract. Pattern electroretinograms were studied in response to stripe patterns of different spatial frequencies and intensities in the pattern-onset and reversal mode by means of a scanning laser ophthalmoscope and a mechanical mirror system (maxwellian view). The stimulus conditions in both procedures were as close as possible: 31 ° square field, 633-nm wavelength and the same equipment for recording. The remaining differences between the two methods were the line and pixel structure in the scanning laser ophthalmoscope and the build- up speed (40 ms in the scanning laser ophthalmoscope and less than 1 ms in the mirror system). This difference was reflected in the response peak times of the pattern electroretinogram, which were up to 10 ms in the scanning laser ophthalmoscope measurement. The pattern-related onset response was smaller with the scanning laser ophthalmoscope, indicating a strong sensitivity to the slow build-up speed, while the offset and reversal responses showed no differences in amplitudes. All differences were found only with the use of high luminances. The results suggest that responses evoked with patterns displayed on a television screen could be faster and larger if stimulators faster than the conventional television standard were used. Because of the smallness of onset amplitudes, the pattern-reversal mode might be better for stimulation in a clinical study when the scanning laser ophthalmoscope is used. Introduction The diagnostic utility of scanning laser ophthalmoscopes (SLOs) has widely improved in recent years [1, 2]. This is true for the evaluation of the mor- phology of the (fundus of the eye fundus topography [3], retinal vessels [4, 5]), for stimulation of the retina with symbols or patterns under visual control (microperimetry [6, 7]), and for eye movement recordings [8-10]. The range of pattern contrast and intensity is much larger with the SLO technique [11 - 13] than with a television monitor. Refractive errors can be compensated within the machine, and the stimulation is not significantly affected by other ocular optical errors. It is possible to generate complex and localized pat- terns [14 - 17] anywhere on the retina (for instance, focal stimulation of the Bjerrum area), including increment (brighter stimuli on dim background) or decrement (darker stimuli on bright background) patterns. With the SLO, it is possible to monitor the fundus with a superimposed stimulus during the whole process of averaging electrophysiologic measurements. Because of the