Artificial Retina Imaging For The Sight Impaired: Sensors and Transducers Robert Jubie April 14th, 2017

Covered in this Presentation: Anatomy of the Eye Pathologies of the Eye How Implants Simulate Vision Types and locations of Implants Design and Construction of Implants Quality of Vision Achieved via Implantation

Anatomy of the Eye Source: http://www.glaucoma.org/uploads/glaucoma_eye_290_b.jpg

Examples of Ocular Pathologies Glaucoma Macular Degeneration Diabetic Retinopathy Retinal Detachment Retinitis Pigmentosa

Categories of Implants Epiretinal Complex Design Requiring External Sensing and Image Processing Direct Stimulation of Ganglia Can be used on very damaged retinas Has FDA Approved Devices Argus II Subretinal Devices in Clinical Trials in US and Approved in Europe Alpha AMS Use Photodiode Arrays Simpler Design Requires Mostly Intact Retina

Location of Implants Johnson Lee J, Scribner Dean A. Electrode Architecture: Meeting the Challenge of the Retina–Electrode Interface

How do Implants Work? Electrical stimulation of cells in the retina Causes “dots” of light in vision Activation threshold of cells is inversely proportional to the distance of stimulation Subretinal implants can remain simple because they use most of the eye’s built in mechanisms for processing imaging Uses arrays of photodiodes to induce current Epiretinal implants directly stimulate ganglia and require external sensing such as cameras to obtain visual information Complex image processing required to create meaningful visual data

Construction of Implants Flexible Designs Feature Sizes ~ tens of μm Polyamide over Silicon Substrate Layer Allows fit to custom curvatures of the retina Reduces available space for electrodes Argus II only accommodates arrays of <100 electrodes Not enough resolution for text or facial recognition Alpha AMS ~1500 photodiodes Allows text interpretation MEMs Based Micro structured springs that fit to eye curvature Closer to retinal cells -> Lower excitation current needed Frail and difficult to implant

Construction of Implants Electrode Architecture: Meeting the Challenge of the Retina–Electrode Interface

Construction of Implants Rigid Designs Allows for higher densities of electrodes Arrays of roughly 5000 devices Large distance between center of implant and retina Can use silicon columns as micro-leads to penetrate retina Glass matrix insulation between leads

Obtainable Vision with Current Implants Vision is Pixelated Degree depends on resolution of electrode array Large, clear texts can be legible with current experimental technologies Varying Degrees of Spatial and Temporal Perception Even low resolution arrays allow navigation through environment Limited Field of View Breadth of electrodes determines field of view Sommerhalder J, Oueghlani E, Bagnoud M, Leonards U, Safran AB, Pelizzone M. Simulation of artificial vision: I. Eccentric reading of isolated words, and perceptual learning. Vision Res 2003;43:269–283.

Going Forward - Conclusions Retinal Implants have improved over the last several years to where implantees can navigate environments and read text There are many approaches to retinal implants but the most state of the art use arrays of photodiodes on a flexible polyamide layer and are implanted subretinally Although resolution has been greatly improved, refresh rates tend to be very slow at < 10 Hz

Sources Sommerhalder J, Oueghlani E, Bagnoud M, Leonards U, Safran AB, Pelizzone M. Simulation of artificial vision: I. Eccentric reading of isolated words, and perceptual learning. Vision Res 2003;43:269–283. Johnson Lee J, Scribner Dean A. Electrode Architecture: Meeting the Challenge of the Retina–Electrode Interface A 4+1 ARCHITECTURE FOR IN VIVO ELECTROPHYSIOLOGY VISUAL PROSTHESIS Alejandro Barriga-Rivera1, Calvin D. Eiber1, Paul B. Matteucci1, Spencer C. Chen1, John W. Morley1, 2, 3, Nigel H. Lovell1, Gregg J. Suaning1 G. Chader; J. Weiland; M. Humayun (2009). "Artificial vision: needs, functioning, and testing of a retinal electronic prosthesis". Progress in Brain Research. 175: 0079–6123. doi:10.1016/s0079-6123(09)17522-2. Artificial vision with wirelessly powered subretinal electronic implant alpha-IMS Katarina Stingl, Karl Ulrich Bartz- Schmidt, Dorothea Besch, Angelika Braun, Anna Bruckmann, Florian Gekeler, Udo Greppmaier, Stephanie Hipp, Gernot Hörtdörfer, Christoph  Kernstock, Assen Koitschev, Akos Kusnyerik, Helmut Sachs, Andreas Schatz, Krunoslav T. Stingl, Tobias Peters, Barbara Wilhelm, Eberhart Zrenner

Five Key Concepts The retina is composed of many cell types and damage to these types determines type of implant that can be used and location Implants can be either flexible and fitting to the retina, or rigid, each having tradeoffs Epiretinal implants stimulate ganglia directly – which requires extremely complex designs and external sensing hardware, Subretinal implants use photodiodes to simulate damaged photoreceptors in the eye – these designs are much simpler and usually consist of implant, ribbon, and wireless power supply State of the art implants have densities of over 1500 photodiodes per implant, which is enough to allow some patients to see movement, differentiate between light/dark objects, or even read some texts

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