Browsing by Author "Lin, Po-Kang"

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A CMOS 256-pixel Photovoltaics-powered Implantable Chip with Active Pixel Sensors and Iridium-oxide Electrodes for Subretinal Prostheses
(2018-01-01)
Wu, Chung-Yu
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Kuo, Po-Han
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Lin, Po-Kang
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Chen, Po-Chun
;
Sung, Wei-Jie
A CMOS implantable chip with 256 active pixel sensors (APSs), on-chip photovoltaic cells, and iridium-oxide (IrOx) electrodes is proposed and designed for subretinal prostheses. In the proposed chip, the on-chip electrode surface is deposited with IrOx by RF sputtering and photolithography patterning. The divisional power supply scheme (DPSS) is adopted to generate sufficient stimulation current whereas the APS is used to enhance the image sensitivity. The proposed chip consists of a 16 x 16 photodiode array with 8 DPSS divisions, control signal generator circuits, and photovoltaic cells. It is designed and fabricated into 180 nm CMOS image sensor (CIS) technology and postprocessed with an IrOx coating. From the electrical measurement results, the fabricated chip has a peak output stimulation current of 16.7 mu A under the equivalent electrode impedance load. The stimulation frequency is 30.2 Hz and the amount of injected charges at each pixel is 3.5 nC. Both image light sensitivity and injection charges are significantly improved. The surface morphology, crystallinity, charge storage capacity, and biocompatibility of sputtering iridium oxide film (SIROF) were investigated. As a result, the SIROF has desirable physical and electrochemical properties that make it suitable for the neurostimulation electrodes on the 256-pixel implantable chip. The 7-month biocompatibility and charge delivery capability of the fabricated chip have been confirmed by electroretinography (ERG) measurement on a Lanyu minipig in in vivo animal tests.
EFFICACY OF INTRAVITREAL INJECTION OF ANTI-VASCULAR ENDOTHELIAL GROWTH FACTOR AGENTS FOR STAGE 4 RETINOPATHY OF PREMATURITY
(2015-04-01)
Cheng, Hui-Chen
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Lee, Shui-Mei
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Hsieh, Yi-Ting
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Lin, Po-Kang
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生醫電子轉譯研究中心
Purpose: To investigate the efficacy of intravitreal injection of anti-vascular endothelial growth factor agents for Stage 4 retinopathy of prematurity. Methods: Retrospective case series study. The medical records of patients receiving intravitreal injection of anti-vascular endothelial growth factor agents for Stage 4 retinopathy of prematurity from January 2007 to May 2012 in Taipei Veterans General Hospital were reviewed. Results: A total of 13 eyes of 7 patients (3 boys and 4 girls) with Stage 4 retinopathy of prematurity were included. The mean gestational age and birth weight were 27.6 +/- 2.6 weeks (range, 24.5-30.5 weeks) and 893.1 +/- 293.2 g (range, 550-1422 g), respectively. The mean age at the time of injection was 38.2 +/- 1.9 weeks (range, 36.0-41.5 weeks) post-menstrual age, and the mean follow-up period was 37.8 +/- 19.5 months (range, 11.0-67.5 months). The active neovascularization regressed rapidly, and the anatomical outcomes were favorable in all patients. One eye developed recurrent retinal hemorrhage with localized retinal detachment 21 weeks after initial treatment, which resolved after a second injection. There were no ocular or systemic complications in these patients. Conclusion: Intravitreal injection of anti-vascular endothelial growth factor agents may be effective as monotherapy or as supplement to failed laser treatment for patients with Stage 4 retinopathy of prematurity without additional surgical intervention. Further randomized controlled trials are necessary to compare the clinical efficacy and safety with other conventional interventions.
Hyperhomocysteinemia in Patients with Polypoidal Choroidal Vasculopathy: A Case Control Study
(2014-10-22)
Cheng, Hui-Chen
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Liu, Jorn-Hon
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Lee, Shui-Mei
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Lin, Po-Kang
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生醫電子轉譯研究中心
Purpose: To determine whether elevated plasma homocysteine and serum high sensitivity C-reactive protein (hsCRP) levels, two established risk factors of vascular diseases, are associated with polypoidal choroidal vasculopathy (PCV). Design: Retrospective case-control study. Methods: One hundred and nineteen consecutive patients with PCV and 119 matched controls were enrolled in a tertiary hospital from September 2008 to June 2013. Plasma homocysteine and serum hsCRP levels were measured. Associations among plasma homocysteine, serum hsCRP levels and PCV were further evaluated using multivariable logistic regression analysis. Results: The median plasma homocysteine level was significantly higher in patients with PCV than in the controls (12.20 mu mol/L vs. 9.80 mu mol/ L, p<0.001). The median serum hsCRP level was slightly higher in the PCV group (0.16 mg/dl vs. 0.11 mg/dl in control group, p = 0.07). After multivariable logistic regression analysis, each 1 mmol/ L increase of plasma homocysteine was associated with a 1.5-fold increase in likelihood of having PCV (OR, 1.54; 95% confidence interval (CI), 1.33-1.79, p<0.001). Conclusions: Hyperhomocysteinemia was associated with PCV and might play a role in the pathogenesis of PCV.
Responses of Rabbit Retinal Ganglion Cells to Subretinal Electrical Stimulation Using a Silicon-Based Microphotodiode Array
(2011-12-01)
Yang, Ya-Ting
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Lin, Po-Kang
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Wan, Chen
;
Yang, Wen-Chia
;
Lin, Li-Ju
PURPOSE. With subretinal prostheses, retinal ganglion cells (RGCs) are activated by electrical stimulation of the retinal neural network. The aim of this study was to evaluate the efficacy of silicon-based solar cells in evoking RGC responses by electrically stimulating the photoreceptor side of an isolated retina. METHODS. A light-bleached retina of an adult New Zealand White rabbit was placed with its photoreceptor side down onto a silicon chip that consisted of a 4 x 4 microphotodiode array (MPDA). The stimulating current was elicited by activating the solar cell with a 532-nm laser light source. Responses of the ON and OFF alpha RGCs on electrical stimulation were recorded extracellularly. Recorded RGCs were then injected with 4% N-(2-aminoethyl)-biotinamide hydrochloride to allow cell type identification. RESULTS. Using a design that includes a circumvented ground electrode, the authors successfully evoked spiking responses by the ON and OFF alpha RGCs in an isolated rabbit retina using low light power to activate the MPDA (equivalent to 39 mu C/cm(2)). The charge density-dependent response and the frequency-dependent pair-pulse suppression were characterized. The spike latency of the RGC responses triggered by electrical stimulation was equivalent to the latency of its light response, which supports the hypothesis that the activation is mediated by the retinal neural network. CONCLUSIONS. Reliable activation of RGCs by electrical stimulation in vitro using an MPDA demonstrates the feasibility of developing solar cell-based subretinal prostheses that potentially could be developed into a power-free device able to restore vision. (Invest Ophthalmol Vis Sci. 2011; 52: 9353-9361) DOI: 10.1167/iovs.11-7808
Responses of retinal ganglion cells to electrical stimulation with a subretinal photovoltaic prosthesis
(2015-06-01)
Tsai, Yueh-Chun
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Kuo, Po-Han
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Lin, Po-Kang
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Wu, Chung-Yu
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Chiao, Chuan-Chin
Short-Term External Buckling With Pneumatic Retinopexy for Retinal Detachment With Inferior Retinal Breaks
(2013-04-01)
Cheng, Hui-Chen
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Lee, Shui-Mei
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Lee, Fenq-Lih
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Liu, Jorn-Hon
;
Kuan, Chieh-Hsiung
PURPOSE: To introduce a new approach for short-term external scleral buckling with pneumatic retinopexy for the management of rhegmatogenous retinal detachment with inferior retinal breaks. DESIGN: Retrospective, noncomparative, interventional case series. METHODS: A review of 33 consecutive eyes of 31 patients who underwent external buckling with pneumatic retinopexy for uncomplicated rhegmatogenous retinal detachment with inferior, retinal breaks from December 2006 through December 2010. An external buckle was made of a 505 sponge sutured along the blunt side of a 279 tyre (MIRA Inc). The buckle was inserted deeply into the inferior fornix without suture after pneumatic retinopexy and was kept in place for 3 days. Primary and final anatomic outcomes, visual acuity, and adverse events were recorded. RESULTS: All patients tolerated the procedure. The mean follow-up period was 24.0 months (range, 9 to 61 months). Primary success, defined as successful retinal reattachment within 6 months without further treatment, was achieved in 29 (87.9%) eyes. All patients attained final retinal reattachment (100%). Overall, the mean best-corrected visual acuity improved significantly at the end of follow-up (0.30 logarithm of the minimal angle of resolution units; Snellen equivalent, 6/12), compared with the preoperative best-corrected visual acuity (0.82 logarithm of the minimal angle of resolution units; Snellen equivalent, 6/38; P < .001). CONCLUSIONS: Short-term external buckling with pneumatic retinopexy is a novel and effective treatment for rhegmatogenous retinal detachment with inferior retinal breaks, with a comparable success rate with other treatment methods. This approach also can avoid complications of long-term buckle implantation. Further comparative cohort studies may be necessary to compare the clinical efficacy with other conventional operations. (Am J Ophthalmol 2013;155:750-756. (C) 2013 by Elsevier Inc. All rights reserved.)
Spatiotemporal integration of visual stimuli and its relevance to the use of a divisional power supply scheme for retinal prosthesis
(2020-02-21)
Tsai, Yueh-Chun
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Wu, Jose Jiun-Shian
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Lin, Po-Kang
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Lin, Bo-Jyun
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Wang, Pin-Shiou
A wireless photovoltaic retinal prosthesis is currently being studied with the aim of providing prosthetic vision to patients with retinitis pigmentosa (RP) and age-related macular degeneration (AMD). The major challenge of a photovoltaic device is its limited power efficiency. Our retinal prosthetic design implements a unique divisional power supply scheme (DPSS) system that provides the electrical power generated by all of the solar cells to only a subset of electrodes at any moment in time. The aim of the present study was to systematically characterize the spatiotemporal integration performance of the system under various DPSS conditions using human subjects and a psychophysical approach. A 16x16 pixels LED array controlled by Arduino was used to simulate the output signal of the DPSS design, and human performance under different visual stimulations at various update frequencies was then used to assess the spatiotemporal capability of retinal prostheses. The results showed that the contrast polarity of the image, image brightness, and division number influenced the lower limit of the update frequency of the DPSS system, while, on the other hand, visual angle, ambient light level, and stimulation order did not affect performance significantly. Pattern recognition by visual persistence with spatiotemporal integration of multiple frames of sparse dots is a feasible approach in retinal prosthesis design. These findings provide an insight into how to optimize a photovoltaic retinal prosthesis using a DPSS design with an appropriate update frequency for reliable pattern recognition. This will help the development of a wireless device able to restore vision to RP and AMD patients in the future.