Source: Richard Glickman-Simon, MD, Assistant Professor, Department of Public Health and Community Medicine, Tufts University School of Medicine, MA
The simplest ophthalmoscopes consist of an aperture to look through, a diopter indicator, and a disc for selecting lenses. The ophthalmoscope is primarily used to examine the fundus, or the inner wall of the posterior eye, which consists of the choroid, retina, fovea, macula, optic disc, and retinal vessels (Figure 1). The spherical eyeball collects and focuses light on the neurosensory cells of the retina. Light is refracted as it passes sequentially through the cornea, the lens, and the vitreous body.
The first landmark observed during the funduscopic exam is the optic disc, which is where the optic nerve and retinal vessels enter the back of the eye (Figure 2). The disc usually contains a central whitish physiologic cup where the vessels enter; it normally occupies less than half the diameter of the entire disc. Just lateral and slightly inferior is the fovea, a darkened circular area that demarcates the point of central vision. Around this is the macula. A blind spot approximately 15° temporal to the line of gaze results from a lack of photoreceptor cells at the optic disc.
1Department of Biochemistry and Molecular Biology, SUNY Upstate Medical University
1Experimental Molecular Biophysics, Freie Universität Berlin
1Faculty of Pharmacy, University of Sydney, 2Department of Nanobiomedical Science & BK21 PLUS NBM Global Research Center for Regenerative Medicine, Dankook University
1Department of Materials Science and Engineering, Massachusetts Institute of Technology, 2Department of Biological Engineering, Massachusetts Institute of Technology, 3Department of Mechanical Engineering, Massachusetts Institute of Technology, 4Department of Neurology, The F.M. Kirby Neurobiology Center, Boston Children’s Hospital, Harvard Medical School
1Department of Nanoscience, University of North Carolina at Greensboro, 2Center for Biotechnology, Genomics, and Health Research, University of North Carolina at Greensboro, 3HORIBA Scientific
1Department of Bioengineering, University of Illinois at Chicago, 2Department of Pathology, University of Illinois at Chicago, 3Department of Biological Sciences, University of Illinois at Chicago, 4Department of Chemistry, University of Illinois at Chicago, 5Department of Nephrology, University of Illinois at Chicago
1Biotactical Engineering, Faculty of Science, Engineering and Technology, Swinburne University of Technology
1School of Mechanical and Aerospace Engineering, Center of Laser and Optical Engineering, Nanyang Technological University, 2d'Optron Pte Ltd
1Biomedical Engineering, Duquesne University, 2Department of Computer Science, University of Missouri, 3Department of Bioengineering, University of Missouri
1Department of Medicine B, University Hospital Münster, 2Institute of Palliative Care, University Hospital Münster, 3Biomedical Technology Center, University of Münster, 4Department of Gastroenterology, Klinikum Bielefeld
1Department of Mechanical and Aerospace Engineering, The George Washington University
1Department of Materials Science and Engineering, Clemson University, 2Department of Materials Science and Engineering, Texas A&M University, 3Department of Electrical and Computer Engineering, Texas A&M University, 4College of Optics and Photonics, Center for Research and Education in Optics and Lasers (CREOL), University of Central Florida, 5Department of Materials Science and Engineering, Massachusetts Institute of Technology, 6Department of Mechanical Engineering, Virginia Polytechnic Institute, 7Microphotonics Center, Massachusetts Institute of Technology
1Department of Psychology, St. Mary's College of Maryland, 2Department of Psychology, University of British Columbia
1Section of Neuroelectronic Systems, Dept. of Neurosurgery, University Hospital Freiburg, 2Laboratoire d'Imagerie et de Neurosciences Cognitives, UMR 7364 Université de Strasbourg, CNRS, 3Faculté de Psychologie, Neuropôle de Strasbourg
1Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, 2Laboratory of Chemical Biology, Eindhoven University of Technology, 3Laboratory of Physical Chemistry, Eindhoven University of Technology, 4Institute for Complex Molecular Systems, Eindhoven University of Technology
Source: Derek Wilson, Asantha Cooray, PhD, Department of Physics & Astronomy, School of Physical Sciences, University of California, Irvine, CA
Light travels at different speeds depending on the material through which it is propagating. When light travels from one material to another, it will either slow down or speed up. In order to conserve energy and momentum, the light must change the direction in which it propagates. This bending of light is known as refraction. Some fraction of the light is also reflected at the interface between the two materials. In special cases, a light beam can be refracted so sharply at an interface that it is actually completely reflected back into the medium from which it was coming.
Lenses make use of the principle of refraction. Lenses come in two varieties with different curvatures: convex lenses and concave lenses. Convex lenses are often used to focus light but can also be used to create magnified images of objects. When a convex lens causes the light rays coming from an object to diverge, the human eye judges the light to be coming from some point behind the actual object from which the light is originating. The image of the object will in this case be magnified. This type of image is called a virtual image. Concave …
1School of Geography, Earth and Environmental Sciences, University of Birmingham, 2Analytical Science, National Physical Laboratory, 3INAC-LCIB, Université Grenoble Alpes, 4CEA, INAC-SyMMES, 5NIMBE, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 6Chemical, Medical and Environmental Science, National Physical Laboratory, 7BAM Division 6.1 'Surface Analysis and Interfacial Chemistry', BAM Federal Institute for Materials Research and Testing, 8Fraunhofer Institute for Ceramic Technologies and Systems
1CEA, LETI, DTBS, LISA, Université Grenoble Alpes, 2CEA, LETI, DTBS, LBAM, Université Grenoble Alpes, 3CEA, INSERM, BIG, Université Grenoble Alpes, 4CNRS, FR CNRS 3425, 5CNRS, UMR 144, Molecular Mechanisms of Intracellular Transport, PSL Research University, Institut Curie, 6TIMC-IMAG
1The ithree Institute, University of Technology, Sydney
1Department of Mechanical Engineering, National Taiwan University, 2Department of Mechanical Engineering, National Taiwan University of Science and Technology
1Department of Chemistry, University of North Carolina at Charlotte, 2Nanosys Inc.
1Department of Human Genetics, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, 2Microscopical Imaging Centre (MIC), Radboud University Medical Center, 3Department of Biology, Universidad Autónoma de Madrid, 4Department of Clinical and Experimental Medicine, Linköping University, 5Department of Pathology, Radboud University Medical Center
1Department of Biomedical Engineering, Oregon Health & Science University, School of Medicine, 2Department of Dermatology, Oregon Health & Science University, School of Medicine, 3Department of Cell & Developmental Biology, Division of Hematology & Medical Oncology, Knight Cancer Institute, Oregon Health & Science University, School of Medicine
1Department of Chemistry and Biochemistry, University of Maryland, Baltimore County
1Department of Biological Psychology, Justus-Liebig-Universität Giessen, 2Dipartimento di Psicologia, Università di Bologna
1Department of Neurology, David Geffen School of Medicine, University of California, Los Angeles, 2W.M. Keck Science Department, Claremont McKenna, Pitzer & Scripps Colleges