Cyclic summation versus m-sequence technique in the multifocal ERG

Abstract

Background: The m-sequence technique is a typical tool for the multifocal ERG. The use of LEDs instead of a computer monitor enables a new technique that merits closer investigation: The cyclic summation technique. The aim of this study was to compare the two methods.

Methods: Six normal right eyes were examined with the RETIscan system using DTL electrodes. With an LED array (display diameter 52 degrees, 103 segments, 1 foveal + 102 arranged in six concentric rings) we studied: (1). first order kernels (m-sequence); (2). 30-Hz flicker responses (m-sequence); (3). 30-Hz flicker responses (cyclic summation). The three methods were tested with a pattern of concentric rings generated by selective deactivation of LEDs (the central LED and rings 2, 4 and 6; rings 1, 3 and 5 remained active). In each case six cumulative measurements (40 s each) were made and stored separately. To determine the signal-to-noise ratio, the average mf ERG response to all active LEDs was divided by the average response to the inactive ones.

Results: 1. Using cyclic summation the signal-to-noise ratio exceeds the signal-to-noise ratio of both m-sequence-controlled stimuli about twofold. This implies also better spatial resolution with the cyclic summation technique 2. Since the signal-to-noise ratio increases faster with the cyclic summation technique than with the m-sequence technique, the gain of time in mf ERG can reach 80%.

Conclusion: As far as the signal-to-noise ratio and measuring time is concerned, the cyclic summation technique outmatches the m-sequence technique in mf ERG.