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L. Yow, J. Xie, C. Cela, G. Lazzi, J. Weiland, S. Tsang, M. Humayun; Modeling of ERG Electrode Current Stimulation. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1076. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Electroretinogram (ERG) recordings provide information on the health of the eye. Inversely, current can be sent via the electrode to the retina to elicit a percept of phosphenes. The potential distribution and activating function maps of the electrodes used to stimulate phosphene perception were modeled and compared to perceptual results in both sighted and retinal degenerate (RD) subjects.
The DTL-Plus electrode (DTL) was compared to the ERG-jet electrode (Jet) by 3-D admittance modeling techniques. The modeled electric potential and activating function on the entire retinal surface were achieved by projecting the potentials in the retina onto a rectangular surface using a spherical to cylindrical transformation. Standard ERG techniques were used OD. Excitation thresholds were titrated and a stimulation current of 1.5x >threshold was used. 5 normal subjects were stimulated by DTL and ERG using a 2 hz alternating monophasic constant current for 30 min. with a 30 sec. break every 5 min. 5 RD subjects, >10 yrs of NLP visual acuity, were stimulated using Jet electrodes. Phosphene patterns were depicted by normal subjects on paper and RD subjects in clay.
All subjects perceived electrically generated phosphenes. Average thresholds for normal subjects were <1 mA for both the DTL (0.59±0.23 mA) and the Jet (0.72±0.18 mA). The average thresholds for RD subjects using Jet electrodes were (3.08±2.01 mA). The difference in threshold was statistically significant (p<0.05). Highest potential and activating function values for the DTL are concentrated on the inferior nasal retina OD which corresponds to an excitation of the upper right periphery of the visual field. The activating function map for the Jet revealed a nasal hemiretinal stimulation pattern resulting in a more extensive right peripheral phosphene. The actual stimulation phosphene locations reported by the subjects corresponded to current models.
Electrical stimulation using standard ERG electrodes activates peripheral retina, requires more current in degenerate vs. normal retina, and can be accurately modeled using numerical techniques.
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