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S. M. Walker, D. Keating, S. Parks; Optimisation of Signal Quality During Multimodal Imaging Using Combined OCT/SLO and Micro-Multifocal ERG. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4522.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate factors affecting micro-multifocal electroretinogram (micro-mfERG) signal quality during multimodal imaging (MMI) using combined scanning laser ophthalmoscope (SLO), optical coherence tomography (OCT) and micro-mfERG in order to determine the optimal recording parameters.
An OCT/SLO scanner (OTI; Toronto, Canada) with an integrated organic light emitting diode (OLED) display was used to provide simultaneous micro-mfERG recording, OCT and SLO imaging of up to the central 24 degrees (multimodal imaging; MMI). A series of MMI recordings with differing micro-mfERG parameters were performed on 10 healthy control subjects. Eyes were tested unilaterally using DTL corneal electrodes. The effect of spatial stimulus resolution on micro-mfERG signal quality was investigated by performing MMI with various micro-mfERG spatial resolutions. The effect of stimulus intensity was assessed using differing OLED luminance levels. Temporal characteristics were tested by inserting blank filler frames into the stimulus sequence. The influence of scattered light was investigated by making certain stimulus regions inactive and at high or low luminance to render neighbouring areas less or more sensitive to scatter respectively.
Micro-mfERG signal quality was assessed according to signal to noise ratio (SNR). Based on our experience with conventional mfERG recordings, a SNR of 25dB or higher was the target signal quality. Without spatial averaging or post processing, the highest spatial resolution which achieved the SNR target was a 19 area stimulus. Recordings using the maximum OLED intensity provided the best SNR. Adding filler frames did not improve SNR. Scattered light from neighbouring areas accounted for at least 20% of local response amplitudes and was most marked in the periphery.
During multimodal imaging, the best quality micro-mfERG signals were obtained using a 19 area stimulus array with full OLED brightness and no filler frames. However, our results suggest that micro-mfERG stimulus delivery using an OLED within the OCT/SLO is not optimal. This may be because the optics of the OCT/SLO are designed to focus a coherent light source, consequently peripheral stimulus areas are distorted which results in an increase in scattered light.
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