We have developed a photoelectric dye-coupled polyethylene film as a prototype of retinal prosthesis, named "Okayama University-type retinal prosthesis. The purposes of this study are to conduct behavior tests to assess vision in Royal College of Surgeons (RCS) rats which underwent subretinal implantation of the dye-coupled film, and are also to reveal the retinal response to the dye-coupled film by immunohistochemistry.Polyethylene films were made of polyethylene powder at refined purity, and photoelectric dyes were coupled to the film surface at higher density, compared with the prototype. The dye-coupled film or the dye-uncoupled plain film, as a control, was implanted subretinally from a scleral incision in both eyes of a RCS rat at 6 weeks of the age. Behavior tests, 2, 4, 6, and 8 weeks after the implantation, were conducted by observing head-turning or body-turning in the direction, consistent with clockwise or anticlockwise rotation of a black-and-white-striped drum around a transparent cage, housed with a rat. After the behavior tests at 8 weeks, rats' eyes were enucleated to confirm the subretinal implantation of the films and were processed for immunohistochemistry. In the behavior tests, the number of head-turning, consistent with the direction of the drum rotation, was significantly larger in RCS rats with dye-coupled film implantation, compared with rats with plain film implantation (P<0.05, 3 repeated-measure ANOVA). The number of apoptotic neurons was significantly smaller in the eyes with the dye-coupled film implantation, compared to the eyes with the plain film (P<0.05, Mann-Whitney U-test). In conclusion, subretinal implantation of the photoelectric dye-coupled films restored the vision in RCS rats and prevented the remaining retinal neurons from apoptosis.
Photoelectric dye-coupled polyethylene film, designated Okayama University-type retinal prosthesis or OUReP™, generates light-evoked surface electric potentials and stimulates neurons. In this study, the vision was assessed by behavior tests in aged hereditary retinal dystrophic RCS rats with OUReP™, retinal apoptosis and electroretinographic responses were measured in dystrophic eyes with OUReP™. The dye-coupled films, or plain films as a control, were implanted in subretinal space of RCS rats. On behavior tests, RCS rats with dye-coupled films, implanted at the old age of 14 weeks, showed the larger number of head-turning, consistent with clockwise and anticlockwise rotation of a surrounding black-and-white-striped drum, compared with rats with plain films, under the dim (50 lux) and bright (150 lux) conditions in the observation period until the age of 22 weeks (n = 5, P < 0.05, repeated-measure ANOVA). The number of apoptotic cells in retinal sections at the site of dye-coupled film implantation was significantly smaller, compared with the other retinal sites, neighboring the film, or opposite to the film, 5 months after film implantation at the age of 6 weeks (P = 0.0021, Friedman test). The dystrophic eyes of RCS rats with dye-coupled films showed positive responses to maximal light stimulus at a significantly higher rate, compared with the eyes with no treatment (P < 0.05, Chi-square test). Electroretinograms in normal eyes of Wistar rats with dye-coupled or plain films showed significantly decreased amplitudes (n = 14, P < 0.05, repeated-measure ANOVA). In conclusions, vision was maintained in RCS rats with dye-coupled films implanted at the old age. The dystrophic eyes with dye-coupled films showed electroretinographic responses. Five-month film implantation caused no additional retinal changes.
Photoelectric dye-coupled polyethylene film, designated Okayama University type-retinal prosthesis or OUReP™, generates light-evoked surface electric potentials and stimulates neurons. The dye-coupled films or plain films were implanted subretinally in both eyes of 10 Royal College of Surgeons rats with hereditary retinal dystrophy at the age of 6 weeks. Visual evoked potentials in response to monocular flashing light stimuli were recorded from cranially-fixed electrodes, 4 weeks and 8 weeks after the implantation. After the recording, subretinal film implantation was confirmed histologically in 7 eyes with dye-coupled films and 7 eyes with plain films. The recordings from these 7 eyes in each group were used for statistical analysis. The amplitudes of visual evoked potentials in the consecutive time points from 125 to 250 ms after flash were significantly larger in the 7 eyes with dye-coupled film implantation, compared to the 7 eyes with plain film implantation at 8 weeks after the implantation (P < 0.05, repeated-measure ANOVA). The photoelectric dye-coupled polyethylene film, as retinal prosthesis, gave rise to visual evoked potential in response to flashing light.
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