Reproducibility of multifocal ERG using the scanning laser ophthalmoscope

Prior to application of multifocal electroretinography (mfERG) using the scanning laser ophthalmoscope (SLO) in a clinical routine setting it is important to determine the reproducibility of this technique in normals during the use of monochromatic red HeNe laser light.

Thirty-five eyes of 35 volunteers (visual acuity > or =0.8) were examined using the SLO for mfERG with two test patterns in a 20-deg diameter field. Multifocal ERG was performed using the RETIscan system with a binary m-sequence technique. Evaluation was performed for the first-order kernel concentric ring segments. Three measurements were performed for each type of sequence (six sequences for seven hexagons, eight for 19 hexagons) with removal of electrodes between the recordings. Stimulus intensity for all subjects was set to 235 cd/m2 (background illumination 20 cd/m2). We used gold-foil electrodes to obtain good signal quality while not disturbing corneal transmission and refraction.

The coefficient of variation for the P1 amplitudes for the center and surrounding ring(s) was 10.4% and 9.3% for seven hexagons and 15.2%, 9.3% and 7.6%, for 19 hexagons, respectively. The corresponding intraclass correlation coefficients varied between 0.59 and 0.77. The CV for the P1 peak times varied between 1.3% and 1.5% for ring analysis in seven and 19 hexagons.

Our data shows that the setup of mfERG with the SLO provides a retest variability comparable with conventional CRT examinations. One advantage is the simultaneous visualization of the fundus with observation of fixation during examination, thereby allowing more confidence in pathological results.