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Alejandra Gonzalez Calle, James D Weiland; Evaluation of electrical stimulation of the retina with optical coherence tomography. Invest. Ophthalmol. Vis. Sci. 2016;57(12):3713.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal prostheses have demonstrated the capability to elicit the sensation of light and to give test subjects the ability to detect motion and the location of large objects. To create more complex shape perceptions, each electrode should be perceived as a small, focal spot, which when combined together can form a complex shape. Long pulse stimulation can be used to achieve focal percepts in patients with RD (Retinal Degeneration) diseases; however, safety is a concern because long pulses require more charge than short pulses to elicit a response from neural tissue. To assess safety of stimulation, high charge density and long-pulse duration stimuli were applied to rabbit retina and OCT images acquired before, during, and after stimulation.
Pigmented rabbits (N=7) were anesthetized and OCT images were taken as control before stimulation. Left eye was used in every rabbit. A return electrode was placed on the rabbit’s head and the stimulating electrode (Platinum/Iridium needle electrode) was placed inside the eye 56 26 away from the retina. Different pulse widths, pulse amplitudes, frequencies, stimulation time and size electrodes were used during these experiments (Table 1). OCT images were acquired every 2 min during and after stimulation. At the end of the experiment FA images were taken to evaluate any vessel leakage, then the eye was enucleated and taken for histology evaluation.
Retinal thickness was measured to assess retinal damage. 7 animals were used during the experiments and different parameters points were evaluated using the same animal. When using 250 in diameter electrode and stimulating for 30 min (Frequency: 333 Hz, Charge Density: 1.63 mC/cm2) we could see an increase in retinal thickness with an initial value of 160.3 2.05 and a final value of 190 0.81 showing an increase on retinal thickness of 19.52 % 1.86% compared to the baseline. A paired t-test revealed a statistically significant increase in thickness (p=0.004). This damage expanded laterally for 1.27 mm 0.19 mm. For the other parameters evaluated, there was not increase of retinal thickness after stimulation.
Preliminary results show that electrical stimulation at very high charge densities cause swelling of the retina within minutes of stimulation. The stimulus level at which swelling was noted is significantly higher than that used for stimulation in humans.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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