INTRODUCTION TO VISUAL PROSTHETICS by Eduardo Fernandez and Richard Normann “The best and most beautiful things in the world cannot be seen or even touched – they must be felt with the heart ” Hellen Keller. 1. Introduction. Loss of vision affects millions of people worldwide and poses extraordinary challenges to individuals in …
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Geoffrey. B. Arden and David J. Ramsey 1. Introduction There is a pandemic of diabetes. More than 350 million people are affected world-wide. In the UK more than 4.2 million people (6.3% of the population) are estimated to be living with diabetes, many without even knowing it (1). In the USA 29.1 million (9.3% …
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Frederic Gaillard and Yves Sauve 1. Introduction Injury to the brain areas concerned with vision can cause a variety of disorders ranging from visual field defects to much more complex deficits like visual agnosia. It all depends on the location and the extent of the damage. Injury to the occipital striate cortex results in corresponding …
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Ralph Nelson and Victoria Connaughton 1. Introduction. Retinal ganglion cells are typically only two synapses distant from retinal photoreceptors, yet ganglion cell responses are far more diverse than those of photoreceptors. The most direct pathway from photoreceptors to ganglion cells is through retinal bipolar cells. Thus, it is of great interest to understand how bipolar …
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Yingbin Fu 1. Introduction. Vertebrates rely on retinal rods and cones for the conventional, image-forming vision while non-image-forming vision is mediated by intrinsically photosensitive retinal ganglion cells (ipRGCs) (see Part II Chapter 7). Rods are specialized for low-light vision. They are extremely sensitive and can signal the absorption of single photons. Cones mediate …
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Helga Kolb 1. General characteristics. Over the last few years, psychophysicists, electrophysiologists, geneticists and anatomists have concluded that there is something unique about the short wavelength system compared with the two longer wavelength systems in the visual system. Fig. 1. Cone mosaic in the fovea where the S-wave or blue …
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Helga Kolb 1. General characteristics. The specialized cone pathways of the central fovea of human and monkey retinas have the least convergence and the greatest resolution capabilities of the visual system. This is accomplished by making the connections as “private” as possible and narrowing them to a one to one relationship in the …
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Helga Kolb 1. Circuitry for cone signals. Cone photoreceptors are the sensors of bright light and different wavelengths of light in the retina. They are sensitive in photopic (bright light) conditions and come in several types according to the structure of the visual pigments or opsins in their outer segment regions. In dichromatic …
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Helga Kolb 1. Rods. Rod photoreceptors and rod-connected nerve cells through the retina are responsible for pathways concerned with night vision and increased sensitivity of our visual system under what is called scotopic conditions (conditions of very little ambient light). Most vertebrates have a preponderance of rod photoreceptors in their retinas and such …
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Helga Kolb Our eyes are marvellous sense organs that allow us to appreciate all the beauty of the world we live in, to read and gain knowledge, and to communicate our thoughts and desires to each other through visual expression and visual arts. Vision is the most fundamental of …
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The Role of Dopamine in Retinal Function Abstract Dopamine (DA) is the major catecholamine in all vertebrate retinas including man. All vertebrates have dopaminergic neurons identified as amacrine cells (ACs) and interplexiform cells (IPCs), with great variations among different species. DA neurons are comparatively rare with density about 10-100 per mm2, which means that they …
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Stuart Trenholm1 and Gautam B. Awatramani2 1Assistant Professor, Montreal Neurological Institute, McGill University, Montreal, Canada: stuart.trenholm@mcgill.ca 2Associate Professor, Department of Biology, University of Victoria, Victoria, Canada: gautam@uvic.ca Abstract Gap junctions are recognized in the electron microscope as dense starchy areas of opposed membrane between two cells. Small tracer molecules such as Neurobiotin pass through the …
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1 Introduction “Nothing in biology makes sense except in the light of evolution” (1). Theodosius Dobzhansky’s insight is especially apposite in trying to comprehend the nature of our rod and cone photoreceptors, and the organization of our retina. Unless we understand how these cells and structures arose, through hundreds of millions of years of evolution, …
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Mahnoosh Farsaii and Victoria P. Connaughton 1. Introduction. The AII amacrine cell is characterized by a multifaceted connectivity and physiology. It is unique among amacrine cells in that it participates predominantly in the vertical flow of information though the inner retina, contributing to center mechanisms, rather than in lateral inhibitory pathways. As its multilayer …
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Helga Kolb 1. General characteristics. Amacrine cells of the vertebrate retina are interneurons that interact at the second synaptic level of the vertically direct pathways consisting of the photoreceptor-bipolar-ganglion cell chain. They are synaptically active in the inner plexiform layer (IPL) and serve to integrate, modulate and interpose a temporal domain to the …
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