INVITED PAPER Microelectronic implants that provide identification of simple objects and motion detection for blind patients have been tested and evaluated; further development is needed for face recognition and reading implants. By James D. Weiland and Mark S. Humayun

ABSTRACT | Electronic visual prostheses have demonstrated requirements for a parallel neural interface and power the ability to restore a rudimentary sense of vision to blind efficiency that make certain engineering challenges impor- individuals. This review paper will highlight past and recent tant to all visual implants. This paper will review the causes progress in this field as well as some technical challenges to of blindness, the microelectronic approaches to treating further advancement. Retinal implants have now been tested in blindness, and technology needs to enable future implants. humans by four independent groups. and cortical implants have been also been evaluated in humans. The first implants have achieved remarkable results, including detection II. CAUSES OF BLINDNESS of motion and distinguishing objects from a set. To improve on Blindness can result from damage to the optical pathway these results, a number of research groups have performed (, aqueous humor, crystalline , and vitreous simulations that predict up to 1000 individual pixels may be Fig. 3) that focuses light on the or damage to the needed to restore significant functions such as face recognition visual neurons that sense light and send visual information and reading. In order to achieve a device that can stimulate the to the brain. We will review only the neural diseases, but it is visual system in this many locations, issues of power con- worth noting that cataracts (opacities in the crystalline lens) sumption and electronic packaging must be resolved. are a major cause of blindness worldwide.1 An excellent review of the retina and vision can be found online.2 KEYWORDS | Electrical stimulation; implantable medical pack- Blindness has a significant impact on the economy. aging; medical implants; neural prosthesis; retinal prosthesis Recent studies have found that only 29% of severely visually impaired persons are gainfully employed, com- pared with a national average of 84% [1]. Persons with I. INTRODUCTION severe earn 37% per year less than their Photoreceptors are the specialized neurons in the eye that able bodied counterparts [2]. The total economic impact convert photons into a neural signal (Fig. 1). The of vision loss in the United States is estimated at nearly photoreceptors are part of the retina, a multilayer neural $68 billion annually.3 structure about 200 m thick that lines the back of the eye. The two most common retinal degenerative diseases that Other cells in the retina process the signal from the result in blindness secondary to photoreceptor loss are age- photoreceptors. Retinal ganglion cells send the processed related (AMD) and retinitis pigmen- signal from the retina to the brain via the optic nerve. tosa (RP). RP is generally more severe, and its symptoms Blindness can result when any part of this visual pathway is appear earlier in life, but AMD is more prevalent. In the damaged by injury or disease. Electronic visual prostheses United States, there are approximately 700 000 new AMD are being developed that can be implanted in different patients; each year, 70 000 of these patients will become anatomical locations along the visual pathway (Fig. 2). While legally blind, with many more suffering significant vision the final implementation of the implant will depend on the loss [3]. AMD results from a slow degeneration of the anatomy of the targeted area, visual prostheses have common photoreceptor cells of the retina, ultimately culminating in death. This is sometimes accompanied by

Manuscript received August 14, 2007; revised January 14, 2008. 1See World Health Organization, www.who.int/mediacentre/ The authors are with Doheny Eye Institute, University of Southern California, factsheets/fs282/en/. Los Angeles, CA 90033 USA (e-mail: [email protected]; [email protected]). 2www.webvision.med.utah.edu/. 3 Digital Object Identifier: 10.1109/JPROC.2008.922589 See http://www.silverbook.org/visionloss.

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Fig. 1. Cross-section of the retina. The photoreceptors (rods and cones) convert photons into neurochemical energy, which is relayed through the retina. The different layers of the retina process the image signal. The output of the retina comes from the retinal ganglion cells, whose axons gather at the optic disc to form the optic nerve. In and age-related macular degeneration, the photoreceptors are degenerated but the other layers of the retina remain. (Image courtesy of Webvision, webvision.med.utah.edu.)

Fig. 2. Human visual system. The optic nerve transmits retinal information to the lateral geniculate, which relays the information to the primary visual cortex (striate cortex or V1). (Image courtesy of Webvision, webvision.med.utah.edu.)

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lating electrode array. Implants in humans have been tested in the retina, visual cortex, and optic nerve. Recent clinical trials of retinal implants have included epiretinal implants [7]–[10], a passive subretinal device [11], and an active subretinal device [12] (see Fig. 4). Passive devices rely on incident light for power, whereas active devices have an external power source. All of the devices currently being tested are manufactured by companies, which have the required quality systems and manufacturing skills to produce robust, medical-grade implants. The trials reviewed below will be referred to by the company that produced the implant. The first clinical trial of a permanently implanted retinal prosthesis was initiated by Optobionics, Inc., in 2000.Thedevicewasapassivemicrophotodiodearray with 3500 elements. Subjects in the passive subretinal trial Fig. 3. Cross-section of a . Light is focused by the cornea do not report pixelized vision, as might be expected if each and lens on the retina. The retina lines the posterior of the eye. photodiode were acting as a photoreceptor [11]. However, (Image from http://www.nei.nih.gov/health/cataract/ some of the subjects have reported improved visual cataract_facts.asp.) function away from the implant site, suggesting that the presence of the implant alone, or coupled with low-level electrical stimulation, induced a Bneurotrophic effect[ the formation of new blood vessels. Individuals afflicted that improved the health of the retina and consequently with AMD will start to have distorted central vision and improved visual function. eventually will lose most vision in the central 30 of visual A prototype epiretinal implant with 16 electrodes is field, rendering them legally blind (less than 20/200 vision). beingtestedbySecondSightMedicalProducts,Inc. RP is a collective name for a number of genetic defects that (Sylmar, CA). This trial began in 2002 and has enrolled also result in photoreceptor loss [4]. More than 100 genetic six individuals with bare light perception secondary to RP. defects have been identified that cause the different forms of Test subjects can use spatial information from the RP. The overall incidence of RP is 1 in 3500 live births. In stimulator to detect motion and locate objects [9]. general, RP strikes the rod photoreceptor cells first, Subjects demonstrated their ability to distinguish between resulting in poor night vision and loss of peripheral vision. three common objects (plate, cup, and knife) at levels Eventually, cone photoreceptors, which mediate color and statistically above chance. Subjects have also demonstrat- daytime vision, are lost, leading to complete blindness. ed that they can discern the direction of motion of a bar Neither AMD nor RP is presently curable through surgery passed in front of the camera. Recent reports involve or treatment, but there are some treatments that can slow detection of the orientation of a black and white grating the progression of AMD [5]. pattern [13]. A subject was able to detect these gratings at Diseases that damage the optic nerve include diabetic 4 increasing spatial frequency up to the theoretical limit retinopathy and glaucoma. In diabetic retinopathy, retinal predicted by the electrode spacing on the retina. blood vessel abnormalities can prevent nourishment from Perceptual thresholds are in general low, compared to reaching neural cells in the retina, leading to ganglion cell the earlier short-term implants [8]. Some subjects have and optic nerve damage. Glaucoma often includes high shown a majority of electrodes with a perceptual intraocular pressure as a symptom. In the past, it was thought threshold below 50 A (1 ms pulse), with a range of that high eye pressure was damaging to the retina and led to 24–702 A(1mspulse)reportedacrossthreesubjects.A ganglion cell and optic nerve loss, but more recently it has second clinical trial of an epiretinal implant, built by been found that even individuals with normal eye pressure Intelligent Medical Implants AG (Zurich, Switzerland), can have optic nerve damage from glaucoma [6]. has recently begun. This implant features a microfabri- A. Visual Prostheses cated electrode array of 49 platinum electrodes on a polyimide substrate. Subjects can see and A visual prosthesis can create a sense of vision by crude shapes that correlate to the applied stimulus [10], electrically activating neural cells in the visual system. The but, since this a relatively recent clinical trial, no prosthesis must convert images from a camera into pat- threshold data or visual task performance with subjects’ terns of electrical stimulation applied to the tissue by an using a camera has been reported. implanted neural stimulator. Visual prostheses are de- An active subretinal device developed by Retina lineated based on the anatomical location of the stimu- Implant GmbH (Reutlingen, Germany) began clinical 4See www.nei.nih.gov/health/. trials in 2006. An integrated circuit (IC) was implanted

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Fig. 4. Retinal prosthesis concept. A retinal prosthesis will capture an image with a video camera. The image data will be processed and wirelessly transmitted to the implanted stimulator, which will stimulate the retina in a pattern. (Image courtesy of Annual Review of Biomedical Engineering, vol. 7, pp. 361–401, 2005.) underneath the retina. The IC had 1500 microphotodiodes, in the visual system. The first experimental work towards a which served to modulate current pulses based on the visual prosthesis began with electrical stimulation of the amount of light incident on the photodiode [14]. This visual cortex using a grid of large surface electrodes. This group had not yet developed telemetry electronics, but has progressed to microelectrode arrays that penetrate instead connected to the subretinal IC using a micro- deep into the cortex. A brief summary of the important fabricated cable that passed out of the orbit and crossed the findings in visual cortex stimulation is given below. skin behind the ear. The cable supplied command and The seminal experiment in this field (and possibly in configuration signals as well as power to the IC. Because the field of neural prosthesis) was performed by G. Brindley such a cable arrangement is a potential infection source, in 1968 [15]. Brindley implanted an 80-electrode device on the implant was limited to 30 days, although one subject the visual cortical surface of a 52-year-old blind woman. continuedbeyondthispoint.Thisimplantalsoincluded Each electrode was connected by a wire to a radio receiver 16 Bdirect stimulation[ electrodes, which were not screwed to the outer bony surface. An oscillator coil was activated by the subretinal IC but were directly connected placed above a given receiver in order to activate the to the cable and were activated by external equipment. receiver via radio frequency and stimulate the cortex via Due to packaging limitations, the subretinal IC did not the induced electrical current. With this system, the function in all of the implants. Direct stimulation elec- patient was able to see phosphenes in 40 different trodes were able to elicit responses in all subjects [12]. positions of the visual field, demonstrating that at least This device uses constant voltage stimulation and the half of the implanted electrodes were functional. This stimulus levels needed to generate perceptions have been experiment showed that an implanted electrical stimu- reported as 1–2.5 V for 3 ms. The active subretinal trial is lation device could restore some degree of vision. relatively recent, and few details of the clinical investiga- However, because surface electrodes were used, large tions are published. stimulus currents were needed in order to produce the Experimental artificial vision systems have also been sensation of light, and the phosphenes produced were employed to electrical stimulate other anatomical locations quite large. A second group using surface stimulation in a

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visual prosthesis has shown similar visual acuity [16] but quality of the image, a greater number of electrodes will be also reported seizures resulting from overstimulation [17]. needed to provide more information at higher spatial Intracortical electrodes were developed in order to resolution.However,aswillbediscussedbelow,even reduce the amount of electrical stimulus current, thus more complexity will be required to restore significant avoiding seizures and producing smaller phosphenes. An visual function. array of stimulating microelectrodes was inserted into the The requirements for a high-resolution retinal pros- occipital cortex of patients who were being treated for thesis should follow from the needs and desires of blind excision of epileptic foci [18]. Phospenes were elicited with individuals who will benefit from the device. Our both surface and intracortical electrodes, but intracortical interactions with these patients have indicated that the microstimulation required 10–100 times less current than visual functions that are most important to the blind surface electrodes. The same group later performed a long- include mobility without a cane, face recognition, and term implant in the visual cortex of a test subject with reading. A number of simulation studies have estimated glaucoma who had been blind for more than ten years. visual task performance for prostheses of varying acuity. The 38 electrode system was implanted for a period of These studies are typically performed in normally sighted four months. The subject was able to perceive phosphenes at individuals who don an apparatus that limits their vision. a predictable and reproducible location of the visual space. Cha et al. developed a system to project a defined number It was also demonstrated that several microelectrodes used of pixels on the fovea of a normally sighted person (1–2 of in combination could evoke the perception of patterns. This visual field) [22]. Foveal projection was used because this project was centered at the National Institutes of Health and group was developing a visual cortex prosthesis; the foveal was discontinued in the 1990s. representation in the primary visual cortex was the target Recent efforts in visual cortex prosthesis have evalu- of their implant. The pixelized vision simulation system ated efficacy of visual cortex stimulation in a nonhuman consisted of a video camera and monitor worn on the head. primate (NHP) model [19]. A stimulating array was The monitor was masked by a perforated film to create implanted in the visual cortex of a monkey. The monkey pixels over a visual angle of 1.7 or less (different masks was trained to reach to a location in the visual field that were used for different angles). Standard visual acuity was illuminated by a light. This area was mapped using testing demonstrated that 20/30 vision could be achieved electrical activity recorded on the electrodes. It was then using 625 pixels in the 1.7 central degrees of the visual demonstrated that electrical stimulation on that electrode field [22]. Mobility testing using 625 pixels showed that produced the sensation of a visual percept in the same test subjects could easily navigate a maze [23]. Reading area, and the monkey was able to perform the same visual experiments also using this system with 625 pixels saccade task with both light and electrical stimulation. determined that reading speeds of 100 words per minute Optic nerve stimulation has been demonstrated in one with fixed text and 170 words per minute with scrolling human test subject [20]. A stimulator connected to a cuff text could be achieved [23]. electrode with four contacts was implanted in an RP Simulations of prosthetic vision with a patient. The cuff electrode encircled the optic nerve, which have yielded similar results. These simulations differ from is about 1–2 mm in diameter. Since the electrodes are on the earlier work because the activated area of the retina was the outside of a very densely packed nerve (1.2 million up to 17 of the visual field, which is similar to the coverage fibers within the nerve), focal stimulation and detailed of some prototype retinal prostheses [2]. Dagnelie et al. have perception are difficult to achieve. Stimulation through a studied pixelized vision using a modified low vision single electrode sometimes produces multiple percepts enhancement system (LVES) to pixelize vision and stabilize throughout the visual field. However, the test subject has the image on the retina (image stabilization is done through adopted a strategy of scanning a head-worn camera to eye tracking) [23]. Normally sighted subjects with pixelized achieve remarkable results in pattern recognition. A similar vision were able to recognize faces at rates that were scanning strategy was used by test subject in the epiretinal significantly above chance with as few as 10 Â 10 pixels implant trial. (60% correct versus 25% chance). When 32 Â 32 electrodes A variety of other visual prosthesis implant configura- were used, the recognition scores improved to over 80%. tions are in development but have not yet been implanted Pixel dropout of 70% led to worse scores that were in humans. Extraocular implants have been developed that equivalent to guessing (dropout means the pixel is turned stimulate the retina through the sclera in animal models off, analogous to a nonfunctional electrode). Using a similar [21]. Initial testing of electrical stimulation in the lateral system (Fig. 3), Hayes et al. studied performance in a geniculate nucleus has demonstrated spatial sensitivity in number of different visual tasks including reading [24]. this visual center [22]. Retinal implants have shown the Reading speeds of 15 words per minute were possible, most promise in clinical trials to date but are limited even with only a 16 Â 16 pixelized view. While this is because they require at least part of the retina to be below normal reading speed, it does approach a level of functional,sothereremainsaneedforimplantsproximal utility that may be acceptable to a blind individual. to the retina. In any visual prosthesis, to improve the Mobility testing with a visual prosthetic simulator suggests

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that a 6 Â 10 array of pixels can be used for navigation reasons. First, it is important to control the amount of through an office environment [25]. charge applied to an electrode for safety reasons [30], [31]. Secondly, no net charge can accumulate on the electrode B. Technology Needs for Advanced Visual Prostheses to prevent corrosion and gas formation [32]. Finally, a New technology is needed to realize an advanced constant current results in a constant electric field in device that effectively stimulates the visual system in tissue, although near a disk electrodes, current distribution 600–1000 locations. A visual prosthesis consists of an changes rapidly with time. Human clinical trials have imaging system to acquire and process video. Power and shown that in some subjects, a majority of electrodes had a data will be wirelessly transmitted to an implant by the stimulus threshold below 50 A (1 ms/phase, biphasic external system. The implant will receive data/power and pulse). Other subjects, whose stimulating electrodes were convert to power and program the implant. The implant further away from the retina, had higher thresholds [8]. stimulator chip will convert digital data to an analog output Although it will not be discussed further here, an which will be delivered to the nerves via microelectrodes. imperative for continued improvement of retinal prosthe- An implanted imager is a prominent variant of this system sis is a surgical technique to consistently position the architecture. This would increase the complexity of the electrodes near the retina. implant but remove data telemetry. Intraocular imaging The power requirements for a retinal implant can be components have been proposed for both subretinal [14] calculated based on the information presented above, and epiretinal [26] implants. All of the components of a although some assumptions must be made. We have very retinal prosthesis will require significant engineering good data on electrode impedance, plus most implants research in order to optimize them for a high-resolution have the ability to record impedance as diagnostic data. implant. In the remainder of this paper, we will focus on We also have precise perceptual threshold data, although engineering challenges in the areas of implant power and this is variable amongst electrodes in a single subject and packaging. between subjects. For the purposes of this analysis, we Efficient use of power is a significant issue for a will assume that we have a 30 K load and a 100 A 1000-electrode visual prosthesis. This is related to three output. The instantaneous power at a single electrode is factors: 1) small electrodes are needed to create focused 0.3 mW. This would result in a power requirement of areas of excitation, 2) the relatively high resistivity of 300 mW if all channels were continuously active, but biological media, and 3) the output requirements for neural stimulation is done with pulses of current. If the neural stimulation. electrode is on for 2 ms (1 ms for each phase of a The first two factors listed above will determine the biphasic pulse) and the stimulus is applied at 60 pulses/s load for the current driver. To achieve a high-resolution (which has been shown to result in fused percepts in visual perception, small areas of the retina must be acute stimulation trials [33]), then this is a duty cycle of activated. This will require small electrodes. One approach 12% and the stimulation power requirement is 36 mW. to determining the best electrode size is to draw an This analysis assumes that all electrodes are active, but the analogy to natural vision. For example, an individual with number of electrodes active and the level of activity will be 20/20 vision can resolve differences of 1/60 of one degree dependent on the images incident on the camera which of visual angle, which translates to 5 montheretina. will reduce the stimulation power requirement. However, Thus, it has been argued that to restore vision to this level, in addition to stimulation power, the implant microelec- one would need 5-m-diameter electrodes. Using this tronics will consume power during operation. For argument, Palanker et al. have estimated that a 100 m example, converting an inductively coupled ac signal into electrode could provide vision equivalent to 20/400 [27]. dc power will consume energy. It is difficult to predict A second way to determine the best electrode size is to rely exactnumbersforpowerconsumptionforanimplant on simulations of prosthetic vision, which predict that with 1000 electrodes, but it is clear that efficient micro- 1000 electrodes are needed to perform desired visual tasks, electronic design will be needed to minimize implant and then optimize the electrode size, total area covered by power. the electrodes (the visual angle covered), and number of Electronic packaging technology must be developed to electrodes. An analysis of this type has been reported protect the active components from the corrosive saline previously [28] and suggests that with 1000 electrodes environment in the eye. The package should be virtually in the macula (center 20 of vision), 100-m-diameter impervious (or hermetic) to water or ion ingress and electrodes are acceptable. This diameter electrode will should protect the electronics for at least ten years. At the result in a tissue resistance of approximately 30 K [29] same time, the package must have electrical feedthroughs due to the relatively high resistivity of neural tissue (vias) that electrically connect the circuitry to the (versus metallic conductors). electrodes interfacing with nerve cells (Fig. 5). However, The output requirements for the current drivers are this technology should not add significant size to the another factor in determining power consumption. Con- electronics since the total implant size needs to be small to stant current pulses are used to activate nerves for several safely fit in the body. This is particularly important for a

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Fig. 5. Packaging schemes for neural implants. (Top) A discrete case is typically used to protect electronic components, but this adds size to the implant. (Bottom) If a hermetic coating can be developed and if all electronic functions can be placed on a single integrated circuit, then device size can be reduced. PCBVprinted circuit board, ASICVapplication-specific integrated circuit, RFVradio frequency. retinal implant, which ideally should fit inside the orbit. most 32 feedthroughs. Feedthrough number and density Also, the various electronic components must be efficient- are a significant impediment to achieving a 1000-channel ly packaged in order to minimize implant size. This last visual prosthesis. requirement is complicated by the large storage capacitor The second type of biomedical implant packaging relies and large inductors typically used for inductive power on using a thin film as coating material. This approach is transfer. more technically difficult to achieve because the coating Two bioelectronic packaging schemes have been process must conformally coat the entire electronics proposed and developed for medical implants. First is a module. If all electronics function can be realized on a discrete shell or capsule in which an electronics module is single system-on-chip, then the coating problem is easier placed. The electronics module consists of ICs and off- since there are few contours and crevices to coat (Fig. 5). chip components such as capacitors, diodes, and induc- But if there are multiple chips bonded together or large tors that are difficult to put on chip (Fig. 5). In this discrete components bonded on chips, then small gaps in scheme, a physical gap exists between the chip and the this bond areas are difficult to coat completely. A second package. This gap usually is filled with an inert gas or is a difficulty in coating is making pinhole free coatings. Even vacuum. Discrete packages add size to the overall unit small holes will allow saline access to active conductors, because the package is typically larger than the chip and leading to corrosion. Both organic and inorganic coatings sometimes involves a complicated assembly process, but it have been developed. Organic materials include films allows for flexibility in fabricating the individual such as epoxies, silicones, and polymers including poly- components in their own process before assembly. imides, polyurethanes, and parylene, which can typically Examples of neural stimulators in clinical use with this be deposited at lower temperatures than inorganic mate- type of packaging are BIONs and cochlear implants. rials. Stieglitz et al. [34] used a parylene coating to protect BIONs use cylindrical glass capsules with feedthroughs to a wireless retinal prosthesis system implanted in a re- an electrode on either end of the implant. Cochlear search animal. The device was not chronically activated, implants typically use ceramic or metal cases and have at but the system was periodically powered to check for

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functionality. After 14 months of implantation, the system coatings continue to be pursued because such a technology could still activate the retina and produce a cortical can potentially result in a packaged device that is virtually response. However, the system was not continuously thesamesizeasthechip. powered during this period, and it is generally accepted that biased lines will drive corrosion. Polymers are in general considered not adequate for protection of active III. SUMMARY circuitry for ten years. Water vapor penetration is too Visual prostheses have potential to treat intractable rapid. Ceramics and glass have better water barrier pro- medical conditions. While the visual perceptions that are perties. These materials include films such as silicon ni- created may not have the fine detail of natural vision, there tride, silicon carbide, polycrystalline diamond, and metal is ample evidence that individuals can learn to use reduced thin films. Semiconductor materials like silicon, silicon input to perform simple tasks. Subjects in these trials can dioxide, or silicon nitride are very popular because they identify simple objects and detect motion. From an are resistant to many corrosive environments. Hetke et al. engineering perspective, one of the more encouraging have demonstrated more than one year of stability of a results of these early trials is the low stimulus thresholds, ribbon cable passivated by a stack of silicon dioxide/silicon which suggest that a larger number of smaller electrodes nitride stress-compensated dielectrics [35]. Xiao, et al. can be used. These early examples are motivating have developed a promising coating based on ultranano engineering research that produces novel technology to crystalline diamond and have shown some evidence of support advanced visual prostheses, which will require stability and biocompatibily [36]. However, the fact that no hundreds of electrodes independently stimulating the commercially available neural implant uses an organic or retina. Among the most significant engineering challenges an inorganic coating as a hermetic barrier suggests that this are efficient delivery of implant power and hermetic approach is still in the development stage. Thin-film packaging of electronics. h

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ABOUT THE AUTHORS James D. Weiland received the B.S. degree, the Mark S. Humayun received the B.S. degree from M.S. and Ph.D. degrees in biomedical engineering, Georgetown University, Washington, DC, in 1984, and the M.S. degree in electrical engineering from the M.D. degree from Duke University, Durham, the University of Michigan, Ann Arbor, in 1988, NC, in 1989, and the Ph.D. degree from the 1993, 1997, and 1995, respectively. University of North Carolina, Chapel Hill, in 1994. He spent four years in industry with Pratt & He is a Professor of ophthalmology, biomed- Whitney Aircraft Engines. He joined the Wilmer ical engineering, and cell and neurobiology at Ophthalmological Institute, The Johns Hopkins the Doheny Eye Institute, Keck School of Med- University, Baltimore, MD, in 1997 as a Postdoc- icine, University of Southern California (USC), toral Fellow. In 1999, he became an Assistant Los Angeles. He is Director of the National Science Professor of ophthalmology at Johns Hopkins. He became an Assistant Foundation BioMimetic MicroElectronic Systems Engineering Research Professor at the Doheny Eye Institute, University of Southern California, Center and the Department of Energy Artificial Retina Project. He Los Angeles, in 2001. Currently, he is an Associate Professor of completed his residency in ophthalmology with Duke Eye Center and ophthalmology and biomedical engineering, University of Southern fellowships in both vitreoretinal and retinovascular surgery at The California. His research interests include retinal prostheses, neural Johns Hopkins Hospital, Baltimore, MD. He stayed on as Faculty at prostheses, electrode technology, visual evoked responses, and implant- Johns Hopkins, where he became an Associate Professor before joining able electrical systems. USC in 2001. He has been a key member on a number of National Prof. Weiland is a member of Sigma Xi. He is a member of the IEEE Academies panels. He has authored more than 120 peer-review Engineering in Medicine and Biology Society, the Biomedical Engineering scientific papers and chapters. He has been invited to participate as Society, and the Association for Research in Vision and Ophthalmology. a Guest Speaker in more than 20 countries. His work on the intraocular retinal prosthesis (Bartificial vision[) has been featured prominently in more than 500 newspapers and television programs, throughout the United States and abroad. He has received 11 patents with numerous patents pending. His work has spawned three companies to date. Dr. Humayun is a member of 11 academic organizations including the IEEE Engineering in Medicine and Biology Society, the Biomedical Engi- neering Society, the Association for Research in Vision and Ophthalmol- ogy, the American Society of Retinal Specialists, the Retina Society, the American Ophthalmological Society, the American Academy of Ophthal- mology, and Biomedical Engineering in Medicine and Biology. He was voted as one of the Best Doctors in America and has received numerous research awards. He was named Innovator of the Year in 2005 by R&D Magazine for his outstanding contributions to engineering.

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