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About this Article
Written by: Andrew Wong
Written on: December 8th, 2003
Tags: electrical engineering, health & medicine
Thumbnail by: Wikimedia Commons
About the Author
Andrew Wong was a junior studying Biology and Computer Science at the University of Southern California in the fall of 2003. Aside from his pre-medical pursuits, he enjoys relaxing at the beach, singing a cappella and snowboarding.
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Volume VI Issue I > Shedding Light on Blindness
Two retinal diseases, Age- Related Macular Degeneration (AMD) and Retinitis Pigmentosa (RP), are the leading causes of blindness in individuals over the age of 65. Despite various treatments such as gene therapy and retinal tissue transplant, physicians have thus far been unable to combat the blinding effects of these diseases. With the knowledge that AMD and RP affect only photoreceptor cells, however, a new approach centering on the retinal neurons' ability to be electrically stimulated is being developed. In this method, physicians propose the implantation of a retinal prosthesis device designed to replace photoreceptor cells that have been damaged by retinal disease. The innovations in silicon microchips and microcircuitry have given ophthalmologists the means to create such prosthetic devices. Current trials have been successful, restoring the patients' abilities to distinguish contrast and differing light patterns. In current trials, patients have been able to distinguish contrast and differing light patterns. These retinal prostheses show remarkable promise for future clinical applications completely restoring vision in patients suffering from AMD and RP. This article discusses two new prosthetic devices: the Artificial Silicon Retina (ASR) and the Multiple-Unit Artificial Retina Chipset (MARC). This article focuses primarily on the development, design, and implementation of an experimental device called the Artificial Silicon Retina.

Introduction

Over 30 million people in the world today are affected by retinal diseases. In fact, Related Macular Degeneration (AMD) and Retinitis Pigmentosa (RP) such as Age-Related Macular Degeneration and Retinitis Pigmentosa are the leading causes of blindness in individuals over the age of 65. While physicians have attempted to treat these diseases using various drugs and therapies, such approaches have as yet to succeed.
In spite of this, recent developments in microtechnology and biomedical engineering, however, could potentially restore sight to millions of individuals suffering from retinal disease. Biotechnology is a new approach in this particular medical field; Such advancements in microcircuitry and biocompatible implant materials have given physicians and scientists the opportunity to develop prosthetic devices that are capable of mimicking the function of damaged retinal cells. In fact, two recently developed prostheses, the Artificial Silicon Retina (ASR) and the Multiple-Unit Artificial Retina Chipset (MARC), show immense potential for restoring vision to AMD and RP patients where other treatments have been unsuccessful.The development and clinical application of one such device called the Artificial Silicon Retina will be the focus of this article.

Background

The Human Eye

The human eye consists of many different structures that work collectively to "preprocess" and "send" images to the brain (see Fig. 1). Light first passes into the eye through the cornea and lens of the eye, which focus the light upon onto the posterior portion of the eye called the retina.
Wikimedia Commons
Figure 1: Diagram of Human Eye.
Distributed throughout the retina are two types of photoreceptor cells: rods and cones [1]. These cells convert the initial light energy that enters the eye into electrochemical impulses signals and initialize the propagation of visual information to the brain via the optic nerve. More specifically, the rod cells respond to varying degrees of light and dark, while cone cells respond to color stimuli. The area most densely populated with photoreceptor cells is called the macula. This region is responsible for receiving and processing the most detailed portion of our visual field and is also the region that is most affected by retinal diseases [2].