EPI-RET: IIP Animal experiment 1mC/cm2 is a reasonable safety level to avoid retinal edema Acute human experiments in 20 RP patients phosphene (+): 19 patients threshold (+): 15 patients perception threshold: 191.5±189.7nC (20-380) Size: match head (36%), coin (35%), apple (23%) in 1m distance, previewed experiment brightness: candle (45%), light bulb (33%) color: white (31%), yellow (30%), blue (22%)

Epiretinal IIP technologie, Hamburg-Eppendorf

Fixation of retinal stimulator glue biochemically unstable; species difference degeneration of inner retina (rabbit) fibrin formation (pig) metal retinal tack invasive to membrane & tissues, expensive material: titanium silicon retinal tack photolithography; mass produce, reproduce easily shaped

Stimulating Electrode Suprachoroidal NIDEK-Osaka University Vitreous Stimulating Electrode Reference electrode

Optic Nerve Stimulator Pros. For severe retinal damage Cons. High density of axons (1.2million/2mm diameter) with tough dura Specialized topological arrangement of nerve fibers UCL (Universite Catholique de Louvain), Belgium Stimulation level: BC  GC  ON  LGN  VC 1998. First human trial in the blind patient due to glaucoma 2004. Second human trial spiral cuff electrode (Au-Ti)

Optic Nerve Stimulator good retinotopic correspondence but poor spatial resolution phosphene location depended on gaze direction phosphene size and position are very different from what could have been expected on the basis of the the retinotopically activated axons in the optic nerve

50° field 10° / Div

Visual Cortex Stimulator Pros. Therapeutic potential is greatest - more wide range of indication, e.g. optic nerve damage Cons. Neurosurgery: It’s no kidding!! Difficulty of maintaining a stable interface More complex topology of neurons Epileptogenic property: occipital lobe epilepsy ? Utah, Dobelle Inst., Kresge Stimulation level: BC  GC  ON  LGN  VC

Visual Cortex Stimulator Dobelle & Mladejovsky (1974) 'acute' 38 experiments, succeeded in 15 patients undergoing brain surgery, using 11 Pt electrode area no. 17 seems the most effective locus for cortical stimulation Dobelle (1974) 'Artificial Vision for the Blind' in Science 64 Pt electrode, 8 x 8 array on 3 mm centers in Teflon ribbon cable matrix pattern recognition was unsuccessful

Visual Cortex Stimulator Dobelle (1976): “'Braille' reading by a blind volunteer by visual cortex stimulation” in Nature 64 Pt electrode, 8 x 8 array on 3 mm centers in Teflon ribbon cable matrix 6 non-interacting phosphenes were selected to form a ‘braille cell’

Visual Cortex Stimulator Normann MEMS hairbrush depth probe Si-array, multi-point stimuli 1.5mm below the surface of the visual cortex RF telemetry intracortical vs. surface stimuli Thresholds : x2 to x3 lower 2-point resolution: x5 closer Small phosphenes Electronic components must be small and resilient Techniques for surgical implantation and recording High insertion speed Avoid tissue injury, inflammation, tissue destruction Topographic relationship poor correlation between stimulating pattern and recognition pattern

Telemetry Simple daylight; Optobionics Wired; Dobelle RF; Doheny-NCSU, Louvain Laser; MEEI-MIT

Chemical stimulation Pros. Cons. “Caged glutamate” Releasing no electric current no heat no oxidation high specificity to soma high spatial resolution high turnover Cons. transscleral device need reservoir pharmacokinetics glutamate excitotoxicity in vivo microfluidic device “Caged glutamate” C60 buckminsterfullerene glutamate conjugate Releasing EXCIMER Ga:N UV LED Stanford, Wayne State Univ.

Image still image vs. moving image - “motion blur” steady image vs. flickering image - “flicker fusion” Essential functions; eye positioning, data compression, contrast enhancement, image remapping & customization How many pixels are required ? 25 x 25 : 20/440 - independent movement 32 x 32 : 20/26 - character recognition with LVA 8bit 8bit 4bit 4bit 320x320 32x32 32x32 8x8

Mapping nonlinearity

SNU Prosthesis Chip I Front Chip II Back Data/Power Receiver Chip Current Stimulator Chip In the year 2004, we showed that…. Back