Design of a high-resolution optoelectronic retinal prosthesis

Abstract

It has been demonstrated that electrical stimulation of the retina can produce visual percepts in blind patients suffering from macular degeneration and retinitis pigmentosa. However, current retinal implants provide very low resolution (just a few electrodes), whereas at least several thousand pixels would be required for functional restoration of sight. This paper presents the design of an optoelectronic retinal prosthetic system with a stimulating pixel density of up to 2500 pix mm(-2) (corresponding geometrically to a maximum visual acuity of 20/80). Requirements on proximity of neural cells to the stimulation electrodes are described as a function of the desired resolution. Two basic geometries of sub-retinal implants providing required proximity are presented: perforated membranes and protruding electrode arrays. To provide for natural eye scanning of the scene, rather than scanning with a head-mounted camera, the system operates similar to 'virtual reality' devices. An image from a video camera is projected by a goggle-mounted collimated infrared LED-LCD display onto the retina, activating an array of powered photodiodes in the retinal implant. The goggles are transparent to visible light, thus allowing for the simultaneous use of remaining natural vision along with prosthetic stimulation. Optical delivery of visual information to the implant allows for real-time image processing adjustable to retinal architecture, as well as flexible control of image processing algorithms and stimulation parameters.

Pulsed laser versus electrical energy for peripheral nerve stimulation

“…From data obtained with electrical stimulation the greater the energy applied, the more fibers recruited, resulting in larger amplitude compound potentials. Electrical stimulation has an exponentially decaying spread of charge radiating from the electrode leading to a graded response when stimulating excitable tissue (For review see: (Palanker, Vankov et al 2005)). Increasing optical energy results in a linear increase in recruitment of axons up to a point, suggesting that the energy is transduced immediately beneath the laser spot and has limited diffusion to surrounding tissue.…”

Elektrot Etkileşimi ve Uyartım Eşiğinin Azaltılmasına Yönelik Sonlu Elemanlar Yöntemi Tabanlı Yeni Bir Retina Uyartım Stratejisi

“…Çözümler uyartım vuruları boyunca 1 µs çözünürlükle gerçekleştirilmiştir. Doku üzerinde ortaya çıkan 1000-3000 V/m aralığındaki elektrik alanın sinir hücrelerinin uyartımında etkin aralık olduğu literatürde raporlanmıştır [38]. Bu göz önünde bulundurularak bu aralıkta elektrik alan üreten uyartım kısıtları optimize edilerek uyartım akımı belirlenmiştir.…”

Current and future prospects for optoelectronic retinal prostheses

“…Charge injection has now been maximised by applying a common bias voltage provided from a gogglemounted radiofrequency coil. To ensure that electrodes are close to target cells, Palanker et al 13 have also developed techniques allowing the retina to migrate very closely to the implant.…”

“…All volunteers reported a round-shaped phosphene in response to transscleral stimulation, and phosphene brightness could be controlled with changes in pulse frequency. 34 As with the Australian Bionic Eye Foundation device, the separation of neural cells from electrodes may cause problems due to overheating, crosstalk, and electrochemical erosion, 13 which may restrict the potential visual acuity of the suprachoroidaltransretinal approach. However, the study by Wong et al 35 in cats using suprachoroidal electrode placement has demonstrated the generation of localised phosphene responses with appropriate electrode configurations.…”

“…Apart from the real-time subsampling and conversion of these images to electrode-stimulation patterns, adaptive image processing will probably be required to adjust the resolution, contrast, and brightness of captured images. Non-uniform stimulation thresholds may be required due to the uneven thickness or wavy structure of a diseased retina, 13 and the possibility of continued remodelling of the retina post-implantation could result in spatial corruption and cryptic synapse formation. 36 Epiretinal implants stimulate the RGC layer directly and these cells expect the output from the pre-processed and filtered visual information (from bipolar and amacrine cells), not a camera image.…”