Multifocal Electroretinography with simultaneous fundus imaging in mice

Abstract

Purpose: This study is designed to assess the applicability of multi-focal electroretinograms (mfERG) with simultaneous retinal imaging by scanning laser ophthalmoscopy (SLO) for evaluation of focal retinopathy in mice

Methods: : mfERGs were optimized in C57/Bl6 mice by varying dark steps between each stimulus and the numbers of equally sized hexagons (7, 19, 37) used. To induce focal retinopathy argon laser photocoagulation of different spot sizes and intensities (1. 100µm, 30J/cm2; 2. 300µm, 10,1J/cm2; 3. 300µm, 30J/cm2) were applied. Eyes were investigated before, 10 days and 4 weeks after focal laser treatment. For each recording stimuli were centred on the optic nerve head and pupil area of simultaneously recorded SLO images. Thereby retinal landmarks could be recognized at different time points. To interpret the mfERG data, the amplitudes of the primary mfERG response are regarded.

Results: The mfERG amplitudes changed significantly by varying stimulus conditions. By adding dark steps between mfERG stimuli the amplitudes got higher. The more hexagons were used the lower became the amplitude for each hexagon. The best spatial resolution was seen using 19 hexagons while higher numbers of hexagons led to a high standard deviation of amplitudes (SEM). The hexagon corresponding the the optic nerve head presented the lowest amplitude of all recorded hexagons in most non-treated mice. In areas of focal laser photocoagulation the reduction of mfERG amplitudes was more pronounced the higher the energy and the lager the spot size was that has been used. These results were reproducible at different time points.

Conclusions: Retinal landmarks like the optic nerve head or areas of focal laser treatment could be detected by mfERGs in mice. The simultaneous acquired retinal images correspond to the topography detected by mfERG. mfERG allowed to differentiate focal laser photocoagulation of various size and laser energy. The lack of a higher spartial resolution and the presence of stray light are limitations to be solved in future work.

Keywords: 508 electrophysiology: non-clinical • 578 laser • 612 neuro-ophthalmology: diagnosis