The Organization of the Retina and Visual System
Ning Tian Introduction The neuronal information of the visual scene that is processed by the retina is conducted to the brain by a set of separate spatio-temporal synaptic pathways. The morphological basis for the formation of these parallel synaptic pathways is the laminar-specific structure of the retina, in which specific subtypes of retinal neurons …
Josh Morgan and Rachel Wong 1. Introduction. Synaptic connections of the vertebrate retina are organized into distinct laminae (Figure 1). In the outer retina, photoreceptors contact horizontal cells and bipolar cells within a single lamina, the outer plexiform layer (OPL). Within the inner retina, synapses between retinal ganglion cells and their presynaptic partners, the …
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 …
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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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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By Helga Kolb, Ralph Nelson, Peter Ahnelt, Isabel Ortuño-Lizarán and Nicolas Cuenca Abstract We summarize the development, structure, different neural types and neural circuitry in the human fovea. The foveal pit is devoid of rod photoreceptors and of secondary and tertiary neurons, allowing light to directly stimulate cones and give us maximal visual acuity. The …
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 …
What is glaucoma? David Križaj Abstract Glaucoma, a leading cause of blindness in the world, can be challenging to diagnose because symptoms often appear at late stage of the disease, and challenging to treat because of the irreversible loss of retinal neurons. The term encompasses a heterogenous group of diseases that are characterized by altered …
Ethan D. Cohen, Ph.D., Abstract Retina prostheses try to reactivate the residual circuitry in a blind patient’s retina to produce a synthetic form of usable vision. Using an array of stimulus electrodes or light-sensitive proteins, the neurons in the degenerate retinal network are activated to elicit a series of light percepts termed “phosphenes”. If …
The Science Behind Myopia Brittany J. Carr and William K. Stell INTRODUCTION Myopia (near-sightedness) is the most common refractive vision disorder in children. It is characterized by blurring of objects viewed at a distance, and is commonly the result of abnormal elongation of the eyeball – which causes the refractive image formed by the cornea …
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Jason Nguyen, MD, Liliana Werner, MD, PhD Introduction The crystalline lens contributes approximately +15 to +20 diopters (D) to the refractive power of the human eye in its non-accommodative state. A further 43 diopters is provided by the cornea (see chapter “Facts and Figures”). So when cataracts occur (almost inevitably in the ageing eye) …
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Crystalline Lens and Cataract Joah F. Aliancy, MD and Nick Mamalis, MD INTRODUCTION The lens of the eye is a biconvex, relatively acellular, optically transparent intraocular structure that with the cornea serves to transmit light to the retina with minimal light scattering (Fig. 1a). Early anatomists viewed the lens as the location of meaningful …
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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% …
Bryan William Jones, Robert E. Marc and Rebecca L. Pfeiffer 1. Introduction Retinal degeneration and remodeling encompasses a group of pathologies at the molecular, cellular and tissue levels that are initiated by inherited retinal diseases like retinitis pigmentosa (RP), genetic and environmental diseases like age-related macular degeneration (AMD) and other insults to the eye/retina …