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K. Nakauchi, T. Fujikado, Y. Terasawa, T. Saito, H. Kanda, J. Ohta, A. Hirakata, Y. Tano; Threshold Current for Retinal Damage by Artificial Retina With Chronic Suprachroidal–transretinal Stimulation . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3197.
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© ARVO (1962-2015); The Authors (2016-present)
We have reported that the suprachoridal transretinal stimulation (STS) was a safe and effective method for an artificial retina in acute experiment (Graefe, 2005), and chronic experiment (ARVO, 2005). In this study, we investigated the threshold current which induced the retinal damage with chronic STS.
A single platinum stud–bump shaped active electrode (<font face="symbol">f</font>=0.2mm), which was embedded in polyimide (2x4mm) and coated with parylene, was implanted into the scleral pocket. The epoxy coated platinum wire (<font face="symbol">f</font>=0.1mm), exposed 2mm at the top, was implanted into the vitreous as a return electrode. For the electrical stimulation, anodic–first biphasic pulses (duration 0.5ms, frequency 20Hz) were used. The applied electric current was 0.7mA, 1mA (n=3) and for control 0mA (n=1). Electric pulses were continuously injected every day during one hour for 14 days. The voltage between the active and return electrode was recorded with oscilloscope to examine the impedance.After the 2–weeks stimulation, the retinal damage was examined by funduscopy and fluoroscein angiography. The rabbit eyes were enucleated for histological study and stained with hematoxyline–eosin. The electrode surface was examined by a scanning electron microscope (SEM) before and after stimulation.
The average voltage between active and return electrode during two weeks was 8.6+/–2.1 V by 0.7mA, and 11.0+/– 0.3 V by 1mA stimulation. No change was noticed on the retina and the choroid with funduscopy, whereas fluorescein angiogram showed window defect in 2 rabbits with 1mA but not 0.7mA stimulation. Histological study showed no retinal damage but a small inflammatory change inside the sclera attached to the electrode in all implanted eyes. The SEM study indicated no significant change on the electrode surface.
With our STS method, the safety current limit by 2–weeks chronic stimulation lies between 0.7 and 1mA.
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