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Torsten Strasser, Tobias Peters, Ahmad Zhour, Doaa Akl, Eberhart Zrenner; A Novel Inexpensive And Preparation-free Wet Electrode For Recording Electroretinograms In Small Animals Based On Super-absorbent Polymers. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2462.
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ERG recording quality is particularly dependent on the type of corneal electrodes used, with the best electrodes often being expensive and not necessarily satisfying all requirements. The need of a simple and effective electrode has led us to develop a new kind of electrode, the marble electrode (ME), made of super-absorbent polymers (SAP). Here we present results achieved with MEs compared to gold ring electrodes.
SAPs absorb aqueous solutions through hydrogen bonding up to 300 times their weight. Maximally swollen, an ME is a limpid sphere of a diameter of 10-20mm and made up of 99% water. Applicability of MEs was studied by comparing ERG results of 5 14wks old Brown-Norway rats, anesthetized with Ketamine (100mg/kg) and Xylazine (6mg/kg). MEs were soaked in water for 5h to a diameter of 11mm, if not stated otherwise. Following pairs were used (OS/OD): 4xME/Gold Ring, 1xME/ME 15mm, 1xME/ME 0.9% NaCl. Inter-session reproducibility was assessed. A modified ISCEV protocol with rod b-wave and phot. flicker series using an Espion e2 system was applied. Electrode impedance was checked before recording. A- and b-wave implicit times/amplitudes, P3 oscillatory potential (implicit time/amplitude), b/a ratio of the scot. standard flash (3cd.s/m²), flicker FA and the half-saturation constant of a V-Log I fit were compared. Corneal injuries were examined in 3 rats by anterior chamber OCT.
MEs produce lower amplitudes but equal implicit times for scot. stimuli compared to gold ring electrodes. SF amplitude of a-wave is reduced ~25%, b-wave ~40%. OP3 amplitude and b/a ratio are decreased ~25%. However, amplitudes are similar to those of DTL electrodes, and intra-eye and inter-session variability is small. Half saturation-constant is ~30% higher in MEs. Photopic flicker amplitudes were generally lower than in gold cup electrodes. Oscillatory potentials were observed to become visible at lower stimulus intensities with MEs. Soaking in saline seems to have no effect on amplitude size. Surprisingly, a larger diameter of the MEs results in lower amplitudes. Anterior chamber OCT showed a corneal abrasion caused by a gold ring electrode.
MEs are inexpensive and easy to place in red-light conditions. Low impedance is achieved easily. Simple handling and small variability making MEs a powerful tool for recording ERG in small animals. However, further research has to be done to investigate the electrical properties of MEs in order to explain findings for reduced phot. flicker responses and earlier appearance of oscillatory potentials. To our best knowledge, this is the first use of electrodes based made of super-absorbent polymers for ERG recording in small animals.
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