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M. K. Kim, A. E. Faulkner, M. Roberts, V. T. Ciavatta, G. Y. McLean, H. Y. Choi, M. T. Pardue; Dose Response to Infrared Stimulation in RCS Rats Implanted With Microphotodiode Arrays. Invest. Ophthalmol. Vis. Sci. 2007;48(13):656.
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It has been suggested that electrical stimulation from microphotodiode arrays (MPAs) implanted in RCS rats promotes preservation of retinal function and structure in degenerating retinas (Pardue et al., 2005). We have previously shown a dose response of the subretinal electrical stimulation by different intensities of visible light. Here, we investigate the dose response of subretinal electrical stimulation induced by exposing the MPA device to infrared (IR) light (870 nm).
RCS rats were subretinally implanted at 21days of age with active MPA devices (Optobionics Corp.) in one eye while the other eye and the eyes of the unstimulated animals served as controls. Implanted eyes were exposed to 20 mW/cm2 IR light (n=4) for 1 hr/wk or 60 mW/cm2 IR light (n=6) for 15 min/wk. Estimated current output from the MPA was 450 µA/cm2 and 1400 µA/cm2, respectively. Pulses were presented for 10 ms duration at 20 Hz. Rats were followed for 4 weeks, and retinal function was assessed by ERGs at the end of the study. Eyes were processed for histological assessment of photoreceptor cell counts.
Active MPA implanted eyes receiving IR stimulation at the 60 mW/cm2 level had significantly greater dark-adapted ERG b-wave response (p<0.001) at bright flash intensities (> -2.4 log cd s/m2) when compared to the eyes receiving no IR stimulation, while the responses from eyes receiving 20 mW/cm2 IR stimulation were intermediate between controls and the high stimulation group. A trend for greater number of photoreceptors in the 60 mW/cm2 group compared to 20 mW/cm2 and control groups was present, but was only significant in locations inferior to the implant.
These results suggest a dose response relationship between current output from the MPA device in response to IR stimulation and preservation of retinal function and structure in the RCS rat. The use of IR stimulation avoids the possible light toxicity caused by high levels of visible light and therefore presents a better option for stimulating the MPA device to induce neuroprotection.
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