Retinal Prosthesis Dissertation - Student Home Pages

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1.1.1 Sub retinal The sub retinal approach is to replace the retina by an array of micro photodiodes underneath the retina (the side adjacent to the choroid) to channel natural sunlight [31-40], the concept is to replicate the processing of the retina. Essentially a subretinal implant would be inserted into the space normally occupied by photoreceptors in a healthy retina. The array of micro photodiodes then provides the stimulation data to the retinal implant. Most, if not all, sub retinal approaches rely on converting the colours of light to greyscale prior to stimulation [41]. This has an inherent flaw as the biological retinal actually processes incoming colour [42] in terms of four perceptions of colour namely red, green, blue and yellow and processes those colours to target `red’ cones, `green’ cones and `blue’ cones. These cones in turn propagate colour intensity of each of those planes of colour to specific retinal ganglion cells arranged in a regular topographical arrangement. The seriousness of this inherent flaw depends quite literally on your point of view inasmuch as to be truly biomimetic i.e. to imitate nature, a retinal prosthesis should target cones; for colour vision. However it seems to be perceived wisdom that achromatic targeting is of adequate sufficiency. The technological limitations driving this approach have been twofold: firstly electrode size; and secondly extra wiring required for the colour approach. Until recently electrode size has not been small enough; in vivo, to accommodate average parvocellular cell size of 10µm and in some cases average magnocellular cells of 80µm [43] i.e. although in vitro electrode size of 10µm has been utilised, typically electrode size in vivo has been typically 50µm or in some case 100µm. As the foveola (fovea pit) extends to 200µm diameter in the centre of the fovea centralis, where the predominance of cones governs visual acuity, it is nonsensical to map those signals out to 50µm electrodes; for colour vision, [5-7, 9, 10, 12-14, 44-48] where the RGC axons are about 1µm in diameter [49]. In the 11 of 200
foveola (fovea pit) there is a one to one correspondence from cone to ganglion cell via the bipolar cell [50] implying that within that limitation retinal processing would concern only colour. Outside that limitation sub retinal processing would need to take into account stimulation biologically initiated from rods, horizontal cells, amacrine cells etc. and hence would be more complex than the epiretinal approach described in the next subsection. 12 of 200
Page 1 and 2: An Address Event Representation (AE
Page 3 and 4: Abstract\Foreword This document pro
Page 5 and 6: Contents An Address Event Represent
Page 7 and 8: --Appendix E FPGA Outputs .........
Page 9 and 10: Figure 48 receiver rtl_16 .........
Page 11: Chapter 1 Introduction/research aim
Page 15 and 16: NB that the photoreceptors of the f
Page 17 and 18: electrodes to be driven implies sti
Page 19 and 20: Typically AER is used as a multi se
Page 21 and 22: Real time - innerpulse relationship
Page 23 and 24: the post processing stage of this w
Page 25 and 26: Appendix C: FPGA Sender chip Append
Page 27 and 28: Red (660nm) R / G Red ( 620750nm )
Page 29 and 30: 1 0 1 1 0 0 1 1 0 1 1 1 Table 3 `xo
Page 31 and 32: Adaptive linear combiner w 0 1 Let
Page 33 and 34: is correct (one class) and -1 (the
Page 35 and 36: x2 Linear separation 1.00 0.90 0.80
Page 37 and 38: This is also the Cartesian co-ordin
Page 39 and 40: 2.4 Comparison to Frame Based Repre
Page 41 and 42: Typical GOP structure (Typically an
Page 43 and 44: point is an event occurs for spike
Page 45 and 46: 2.5.1 Files in Appendix A “ycut.m
Page 47 and 48: MPEG-2 setup AER setup Camera Camer
Page 49 and 50: 2.6.2 FPGA representation of epi_re
Page 51 and 52: Chapter 3 Concepts An epiretinal im
Page 53 and 54: AER Transmission lines INPUT image
Page 55 and 56: electrical pulse generated is calle
Page 57 and 58: Figure 25 Retinal colour processing
Page 59 and 60: cells to modulate this luminance pa
Page 61 and 62: L+ M- + - R-G G-R B-Y Y-B Note: L(r
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3.6.2 Retinal operations Light reac
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quantified by number of cycles pres
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(Where * is the convolution operato
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T frame C * R * M p Tpacket i.e. Tp
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e relaxed and from (2) the temporal
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one tw o three four five six seven
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3.8.1 Other test images For other b
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Tspike (4ms) Ispike (16ms: interspi
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INDIGO ORANGE YELLOW MAGENTA CYAN B
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4.1 Sender concepts From chapter on
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pixel must equate to 0.02/1024 i.e.
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Clocking hierarchy (32 by 32 image)
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the number of address bits will alt
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Translation report, (3) Map report,
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90 of 200 CLKIN_IN RST_IN pixelcloc
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incorporate colour planes for each
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Chapter 5 Receiver chip The followi
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5.2 Power Analysis Xilinx FPGAs hav
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98 of 200 produce_wire _outputs Ins
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5.5.1 Incoming (short) AER stream T
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Receiver Red plane r1 DAC (4-bit) T
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5.8.2 Electrode size and positionin
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sequence of wiring from the receive
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does this is to inject an equivalen
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6.2.2 Envisaged retinal array This
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a monochrome camera in this space i
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632mW) thus extending battery life
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For the implemented/structural case
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The sender and receiver circuitry p
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Bibliography 1. Woodburn R. Murray
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38. Banks, D.J., P. Degenaar, and C
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74. Freeman, J.A., Skapura, D. M.,
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109. Weiland, J.D., et al. Progress
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141. Indiveri G. Chicca E. Douglas
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172. Singh, P.R., et al. A matched
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206. Stieglitz, T., et al. Developm
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xmixedsource; numberOfFrames = 8; f
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%check {k} =imread (['D:\abc\subima
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%Two for loops the first (outer loo
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%Row break rr6c1=000; rr6c2=000; rr
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--Appendix B FPGA Test setup librar
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stream_blue_pulse_count: out std_lo
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DVI_XCLK_P clock_25MHz, spike_cloc
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use IEEE.STD_LOGIC_UNSIGNED.ALL; --
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--Appendix C FPGA Sender chip libra
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-- else -- resit '1', CLKDV_OUT =>
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FPGA Receiver (structural) chip --A
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FPGA Receiver (structural) chip --E
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FPGA Receiver (structural) chip --r
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FPGA Receiver (structural) chip blu
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FPGA Receiver (structural) chip con
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FPGA Receiver (structural) chip --s
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FPGA Receiver (structural) chip --
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FPGA Receiver (structural) chip --
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FPGA Receiver (structural) chip IO_
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Number with an unused LUT 18 219 8%
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IO Utilization: Number of IOs: 26 N
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The Slice Logic Distribution report
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Router effort level (-rl): Standard
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oming_clock | HOLD | 0.519ns| | 0|
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Part | xc5vlx50tff1136-3 | Process
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Selected Device: 5vlx50tff1136-3 Sl
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used in combination with MAP -timin
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Data Sheet report: ----------------
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“For these implantable devices to
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microstimulator with a 1:4 demultip
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“Medical experiments have estimat
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A Retinomorphic Vision System “In
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“The common language of neuromorp
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