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Human Visual System and Retinal Blindness•
• Retina is a light sensitive neural network
• Diseases such as Retinitis Pigmentosa (RP) and Age-related Macular Degeneration (AMD) primarily affect the photoreceptors, are both presently incurable, and render 100,000s blind each year
Webvision, Kolb, Fernandez, and Nelson, 2003.
Retinal Prosthesis - Epiretinal vs. Subretinal
EpiretinalLess disruptive to the retina.More flexibility in component placementMore complex stimulus algorithms required
SubretinalIn natural position of photoreceptorsDisruptive to retinaDevices relying on incident light for power cannot generate effective stimulus
State of the Art – Retinal Prostheses• Epiretinal and Subretinal at Investigational
Device Exemption Stage• Epiretinal - encouraging results, but better
technology required• Subretinal – No direct evidence demonstrating
functional electrical stimulation, but patients report subjective improvements in vision
Optobionics ASRTM Second Sight, Model ITM
Overview
Basics of Electrical Stimulation of NerveLimits on stimulating electrodes
Development of a Model 1 retinal prosthesisDisease targetsEarly clinical trialsPreclinical research to specify designClinical trial with implantable system
Future work
Electrical Stimulation of Nerve
Electrode-Retina Interface Design ParametersElectrode diameter.Electrode position.Stimulus waveform
Ganglion Cell LayerBipolar Cell Layer
Photoreceptor Layer
Stength Duration Curve
S1 - M2
0
100
200
300
400
500
600
0 2 4 6 8 10
ms
mic
roA
mps
Dose –Response Curve
M5, 6-27-02
0
2
4
6
8
10
12
0 100 200 300 400 500 600
pulse amplitude (uA)
Perc
eive
d Br
ight
ness
Is a retinal prosthesis feasible?
Electrical stimulation of globe in humans with RP can elicit flashes of light but….are any retinal cells left to stimulate? Or
does stimulation of the globe actually stimulate optic nerve?can focal perceptions be created? Or will
people see only flashes that make no sense?
Mean Cell Count from Post-Mortem RP Eyes
Intraocular Retinal Prosthesis Group © 2000
Group Age,y OuterNuclearLayer
InnerNuclearLayer
GanglionCell Layer
Moderate 73.56±11.19 12.91±17.59* 37.61±10.45 9.21±4.2*
Severe 76.17±8.89 2.33±2.95* 33.37±9.71* 5.72±4.13*
Normal 75.58±10.12 46.9±12.73 42.56±11.56 19.16±5.91
P (UsingF test ofVariance)
0.83 <0.01 0.08 <0.001
Ganglion Cell Layer
05
1015202530354045
-1500-1300-1100
-900-700-500-300-100 100 300 500 700 900110013001500
Eccentricity (µm)
Num
ber o
f Cel
ls
ControlGA
Inner Nuclear Layer
0
20
40
60
80
100
120
140
-1500-1300-1100
-900-700-500-300-100 100 300 500 700 900110013001500
Eccentricity (µm)
Num
ber o
f Cel
ls
ControlGA
Outer Nuclear Layer
0
10
20
30
40
50
60
70
-1500-1300-1100
-900-700-500-300-100 100 300 500 700 900110013001500
Eccentricity (µm)
Num
ber o
f Cel
ls
ControlGA
Condition of retina in RP
Cell counts indicate inner retina survivalMore recent studies of RP shows significant
alteration of retinal circuitry (Marc, 2003)Glial sheath between inner retina and subretinalspaceAnomalous rewiring and cell migration complicates transformation between image and stimulation pattern
Intraocular Retinal Prosthesis Group © 2000
Summary Data from Acute Trials
Intraocular Retinal Prosthesis Group © 2000
Charge (µC)ColorPerceptVisionConditionSubject
0.2WhiteFireflyLPRPJL
1.4WhiteBoxLPRPJT
1.2WhitePinLPRPHW
1.0YellowPinLPRPVO
2.4BluePinLPRPCS
0.3WhitePin20/400AMDAB
1.1WhitePinNLPRPBH
1.8YellowPinLPRPRJ
1.6YellowPinLPRPBC
2.8YellowPeaLPRPPS
6.0WhitePencilNLPAMDWG
3.2YellowPinLPRPRS
0.16YellowMatchheadNLPRPCC
0.95??LPRet-DegenAD
0.4Yellow-GreenLetterNLPRPHC
Electrical Stim in Normal Eyes
In eyes scheduled for removal (cancerous), artificial, focal photoreceptor loss created.Electrical stimulation in retina with
photoreceptors resulted in large, dark perceptionElectrical stimulation in retina without photoreceptors resulted in small, light percepts
Conclusions from Early Human Studies
Degeneration not uniform across retina, most severe in the photoreceptorsElectrical stimulation of retina in blind humans suggest retinal prosthesis possible:
Focal perceptsSpatial correlation between electrode position and percept location
Threshold stimulus current high: 600 uA for 1 ms on average.
Preclinical studies
Chronic implant studies to assess safety of implantation and stimulation, surgical attachment methodsIsolated retina studies to study stimulus thresholds
Chronic Stimulation
180 uA and 90 uA pulses applied, 8-10 hours/day, 60 pps.Histology shown from retina under electrode array after 60 days of stimulation over 4 months of implantation.Morphometric analysis underway on 3 normal and 3 RCD1 dogs that underwent 60-120 days of stimulation
Cortical Recording Methods
After completion of stimulation protocol, subdural electrode implanted.Synchronization of electrical stimulus with data acquisition system.100 averages, multi-channel stimulus.
EER elicited by retinal stimulator
-60
-40
-20
0
20
40
60
0 100 200 300 400 500 600
msec
mic
roV
olts A
BCD
Electrical stimulation of isolated retina
Measure threshold stimulus for retina ganglion cell responseCompare normal vs. diseased retinaJ.S. Shyu, M. Maia, T. O’Hearn
RecordingElectrodePair
1.5-2 mm
Optic Disc
StimulatingElectrodePair
RGC Axons
Isolated Retina: Electrode Position
Stimulating Multi-microelectrode Plate( MMEP)
retina
Recording electrodes
Stimulating Macroelectrodes
Isolated Retina: RGC responses
Electrical Stimulation and Induced Responserd Retina
-3
-2
-1
0
1
2
3
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0
Time (msec)
µVo
lts
cathodic(1mS)
interphase delay (3mS)
anodic(1mS)
measured response latency
Isolated Retina: Stimulus Thresholds
2.69 +/- 0.31 ms
2.11 +/- 0.43 ms
Stimulus Latency(P=0.0278)
111.2 uC/cm261.2 uC/cm2Charge Density
54.57+/-12.45 uA
30.04 +/-11.43 uA
Stimulus threshold(P=0.0597)
rdNormal
Results – Isolated Frog Retina
Stimulus Duration (msec)
0.01 0.10 1.00 10.00 100.00
Cur
rent
Thr
esho
ld (u
A)
10
100
1000
10000
Cadmium
Dark
Light
Summary from other studies
Humayun 200310-1000 nCPerceptionEpiretinal Blind Human, Chronic
Zrenner 200450 nCCortical responseSubretinal Stimulation, Normal Cat
Hesse 200014 nCCortical responseEpiretinal Stimulation, Normal Cat
Stett 19999 nCRGC responsesSubretina, isolated chick retina
Grumet 20002 nCRGC responsesEpiretinal, Isolated Normal Rabbit retina
Rizzo 2003300-500 nCPerceptionEpiretinal, Blind Human Acute
Humayun 1996600 nCPerceptionEpiretinal, Blind Human Acute
Lead AuthorThresholdDetection MethodModel
Conclusions from preclinical studies
Device can be safely implanted on the retinaElectrical stimulation up to 0.1 mC/cm2 does
not damage retinaStimulus thresholds in animal models 1 order of magnitude less than in humans
Prototype Human Retinal Prosthesis
Retinal Implant Surgery
OCTCan provide quantitative information about retina-implant interface.
ElectrophysiologySF VERs were non-recordable at every session. Sub-threshold EERs were non recordable when using lowest levels.
Electrophysiology
07/12/02
L7
L8
L5
L6
L4
L3
L2
M5
M7L1 M3
M6 M2
M1
M4M8 All at 10 cu-50 cu
-10 cu
baseline
Longitudinal Series – Baseline EER
N1-P14.49
N1-P16.05
N1-P18.78
7 electrod.base.-10cu691 µamp
(98.71)
8 electrod.1791 mamp
(223.87)
8 electrod.1111 µamp
(138.87)
Electrophysiology
03/12/02
06/19/02
07/09/02
HEC01 Spatial Map - Horizontal
M1M5
M6
M7
L5
L7
L1
L3
L2
L6
L4
L8
M2
M3
L6 L2
L1
L4
L3
M2
M4
M6
M8
M5 M1
M7 M3
L7
L5
L8
Patient Reported LocationsExpected Results based on Retinal Location
HEC01 Spatial Map - Vertical
M1M5
M6
M7
L5
L7
L1
L3
L2
L6
L4
L8
M2
M3L6 L2
L1
L4
L3
M2
M4
M6
M8
M5 M1
M7 M3
L7
L5
L8
Patient Reported LocationsExpected Results based on Retinal Location
Strength Duration CurvesS1 - M2
0
100
200
300
400
500
600
0 2 4 6 8 10
ms
mic
roA
mps
S1 - M5
020406080
100120140160
0 2 4 6 8 10
ms
mic
roA
mps
L2
0200400600800
1000
0 2 4 6 8 10ms
mic
ro A
mps
• Chronaxie 1-2 ms
Stimulus Thresholds
10 - 91CS
43 - 679YSL
28-949HEC
Threshold range, Day 1(in uA, 1 ms, biphasic pulse)
Subject
Response Thresholds
Computer Controlled TestingTest type HEC01 YSL02 CS03
Sequential activation
4AFC (25%) 16/24 (67%) 28/30 (93%) 20/40 (50%)
Form vision (Row vs. column)
2AFC (50%) 19/32 (59%) 29/30 (97%) 23/30 (77%)
Spatial Location 2AFC (50%) 79/109 (72%)
60/60 (100%) 40/60 (67%)
Object location
Object Recognition
Rows and Columns
Camera Tests
Camera still Test type HEC01 YSL02 CS03
Lights on/off 2AFC (50%) 10/10 (100%)
20/20 (100%)
9/10 (90%)
Moving directions
4AFC (25%) 4/8 (50%) 26/30 (87%) 12/30 (40%)
Camera Tests
19/30 (63%)22/30 (73%)5/10 (50%)4AFC (25%)L position
19/30 (63%)22/30 (80%)40/60 (67%)3AFC (33%)Objects recognition (plate, knife and cup)
31/40 (78%)34/40 (85%)23/30 (77%)4AFC (25%)Counting/finding objects (Ø, R, L, R+L)
23/30 (77%)30/30 (100%)9/10 (90%)3AFC (33%)Finding objects (Ø, R, L)
CS03YSL02HEC01Test TypeScanning
Multi-Pixel vs. Single Pixel
Camera set to either map a single pixel to all electrodes or to map individual pixels to individual electrodes12 cases (4 visual tasks x 3 subjects)
2 showed statistically higher accuracy with multi-pixel setting10 were not statistically different (5 better accuracy, 3 same, 2 worse)
Figure 8. Panel A. Height above the retina versus impedence. Panel B. Height above the retina versus threshold (on log axes). The shaded gray shows the amount of the height above the retina that can be attributed to the thickness of the electrode
S2aS2bS3
Height above retina (mm)
Impe
denc
e (kΩ
)
Height above retina (mm)0.2 0.5 1 1.5 20
10
20
30
40
50
60
0.2 0.5 1 1.5 25
1020
50
100200
5001000
Thre
shol
d (µ
Am
ps)
A. B.
Simulations of prosthetic vision
Cha, Horch, and Normann simulated pixelizedfoveal vision.
25x25 – easy mobility, 100 words/minute reading
Simulation of retinal implant16x16 macular pixels – 15 words/minute reading (Hayes, et al)10x10 face recognition above chance (Dagnelie, et al)32x32 80% face recognition (Dagnelie, et al)
Simulation of Prosthetic Vision
Retinal Prosthesis – Systems Level Description
External camera/image processor detects image and performs conversion to digital informationTelemetry link between external and implanted unitsImplanted unit recovers power and dataImplanted unit applies commanded stimulus patternto the retina via amicroelectrode array onthe surface of the retina
DOE Implants – PDMS electrode
Goal: To develop a PDMS substrate stimulating electrode Progress:
Four normal sighted dogs were implanted. Three of them have been followed for 3 months, 2 months and 1 month. Multilayer cable PDMS test devices were received and evaluated.
Implantation of LLNL device #4
Postoperative 1st month OCT imaging (horizontal scan)
Postoperative 1st month OCT imaging (vertical scan)
DOE Implants – PDMS Electrode
#2 LLNL dog, postoperative 2nd month, OCT imaging
#2 LLNL dog, postoperative 3rd month, OCT imaging
#3 LLNL dog, postoperative 1st month, OCT imaging
#3 LLNL dog, postoperative 2nd month, OCT imaging
DOE Implants – PDMS Electrode
DOE Implants – Spring arrayGoal: To develop silicon based electrode array with MEMS springs for z-axis alignment
Progress: Received two samples of PDMS frame without spring loaded electrodes
Plan: When spring devices received, perform acute and chronic experiments to assess mechanical interface and surgical biocompatibility
Retinal Implant – MEMS Component
microelectronics
electroplated or assembled electrodes
bulk micromachinedelectrode seats
surface micromachinedsprings(polymer) frame
flexible frame for attachment
micromachined electrode array (silicon substrate)
retina
posts for assembly and electrical interconnect
electrodes
flexibleinterconnecttack
antenna
inner-eyeelectronics
Conclusions
Current clinical trial has produced promising results
Low thresholds on some electrodesCorrelation with height from retinaSubjects can sense motion, recognize objects
Active research projects working towards higher density devices