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Ethan D. Cohen, Anant Agrawal, Megan Connors, Barry Hansen, Hamid Charkhkar, Joshua Pfefer; OCT Imaging Of Retinal Damage In Real-Time Under A Stimulus Electrode. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4925.
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© ARVO (1962-2015); The Authors (2016-present)
To study the effects of electrical overstimulation of the local retina directly under a stimulus electrode in real time using a novel imaging method.
Using an 855 nm Fourier Domain optical coherence tomography (OCT) system and a superfused retinal eyecup preparation, we obtained serial B- and C-scans of the rabbit retina under an optically transparent electrode during epiretinal electrical stimulation. A saline-filled fluoropolymer tube electrode (0.4mm i.d.) was centered above the inner surface of the retina to deliver stimulation pulses. During imaging, 50Hz trains of biphasic (cathodic-anodic) constant current pulses 1msec/phase (25-749 µC/cm2/phase ) were applied to the retina for 5 minutes. After imaging, the stimulated region was stained with the nuclear binding dye propidium iodide to reveal cytotoxic damage.
Pulse train stimulation at charge densities of 44 -133 µC/cm2/phase had little effect on the retina, however, trains of 442 µC/cm2/phase or greater caused a swelling of the local retina under the stimulus electrode. During overstimulation, the relative reflectivity of the local inner plexiform layer and inner nuclear layer both rapidly increased in a dome-like region with an irreversible time course suggesting pulse-induced cellular damage. More distally below the electrode, we observed a ring-like pattern of retinal detachment and swelling in the subretinal space near the pigment epithelium. Retinal regions showing swelling and hyperreflectivity in the OCT image also showed propidium iodide staining suggesting electroporative damage was present. The damaged region always matched the diameter of the electrode lumen.
We have developed a novel method to analyze overstimulation of the retina using OCT imaging through a transparent tube electrode. Our distal damage results suggest that electrical currents may pass through the retinal tissue in a non-homogeneous manner. This OCT imaging method may be useful for studying overstimulation of other brain regions.
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