DOCSLIB.ORG

Lecture Aims to Explain: 1. Human Eye Anatomy 2. Optical Power of a Lens

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Lecture Aims to Explain: 1. Human Eye Anatomy 2. Optical Power of a Lens Lecture 10: The Eye Lecture aims to explain: 1. Human eye anatomy 2. Optical power of a lens 3. How eyes work 4. Correction for simple faults in human vision Human eye anatomy Human eye anatomy Light passes through transparent tissue cornea first element in the eye's focusing system Then iris controls the amount of light entering the eye The adjustable crystalline lens – a biconvex body helping to focus the light on retina a layer of light-sensitive tissue at the back of the eye. The retina contains light-sensitive cells called photoreceptors, which translate the light energy into electrical signals fed into optic nerve for delivery to the brain. Photoreceptors in the retina: cones and rods Rods ~120 million on the retina, fast and sensitive “black & white” light detectors, responsible for vision in reduced light levels Cones ~6 million on the retina, slow and less sensitive “colour sensitive” light detectors Rods ~ 100 – 1000 times more sensitive to light than cones Optical power of a lens Optical power of a lens Each surface bends the incoming rays: the more the bending the “stronger” the surface The lens power is defined as the reciprocal of the focal length: 1 1 1 D = = (n −1) − f R1 R2 The unit of optical power is the inverse metre or the Diopter symbolised by D How eyes work Accommodation: fine focussing Eye diameter ~25mm How can the lens system be adjusted so that images of objects at different distances are always obtained on the retina? Object far away Object near The answer was first suggested by Hermann von Helmholtz working in Berlin in 1850s. His theory remained unchallenged until the end of the 20th century Mechanism of accommodation In the human eye accommodation is carried out by changing the focal length of the crystalline lens: this would always allow to obtain the image on the retina Object far away: muscles Object near: muscles relaxed pulling out the lens contracted “squeezing” the making it flat (larger curvature lens making it bulge (smaller radius, less strong lens) curvature radius, stronger lens) Near point: closest distance at which an eye can see. Also termed least distance of distinct vision ~25 cm for a “normal” eye Correction for simple faults in human vision Eyeglasses were probably invented in the late 13th century in Italy. Mentioned in the 15th century by the German cardinal Nicholas Cusa, and ceased to be novelty in the late 15th century. Myopia or near- sightedness Myopia occurs when the eyeball is slightly longer than usual from front Object in infinity to back. This causes light rays to focus at a point in front of the retina, rather than directly on its surface. Far point: for unaccommodated eye, object point whose image lies Distant object on retina For a “normal” eye far point is at infinity No accommodation for all all for 3 examples No accommodation Myopia can be corrected with Far point negative lenses Hypermetropia or far- sightedness This vision problem occurs when Object in infinity light rays entering the eye focus behind the retina, rather than Noaccommodation directly on it. The eyeball of a farsighted person is shorter than normal. Many children are born with Near point hyperopia, and some of them "outgrow" it as the eyeball lengthens with normal growth. Can be corrected with positive lenses Maximum accommodation Maximum 25 cm (near point for “normal” eye) SUMMARY Imaging in human eyes could be understood by considering how a system of two lenses works: one fixed lens in the outer shell of the eye, and one adjustable lens inside the eye. In humans accommodation, a process of obtaining an image on the retina, is carried out by adjusting the focal length of the adjustable crystalline lens inside the eye. Simple faults in human vision occur because the focus of the lens system in the eye can not adjust as required to obtain images on the retina. Can be corrected with additional lenses. The lens power is measured -1 1 1 1 in m or Dioptres (D) and is = = − − defined as the reciprocal of D (n 1) the focal length: f R1 R2 .
Load more

Recommended publications
  • Te2, Part Iii
    TERMINOLOGIA EMBRYOLOGICA Second Edition International Embryological Terminology FIPAT The Federative International Programme for Anatomical Terminology A programme of the International Federation of Associations of Anatomists (IFAA) TE2, PART III Contents Caput V: Organogenesis Chapter 5: Organogenesis (continued) Systema respiratorium Respiratory system Systema urinarium Urinary system Systemata genitalia Genital systems Coeloma Coelom Glandulae endocrinae Endocrine glands Systema cardiovasculare Cardiovascular system Systema lymphoideum Lymphoid system Bibliographic Reference Citation: FIPAT. Terminologia Embryologica. 2nd ed. FIPAT.library.dal.ca. Federative International Programme for Anatomical Terminology, February 2017 Published pending approval by the General Assembly at the next Congress of IFAA (2019) Creative Commons License: The publication of Terminologia Embryologica is under a Creative Commons Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0) license The individual terms in this terminology are within the public domain. Statements about terms being part of this international standard terminology should use the above bibliographic reference to cite this terminology. The unaltered PDF files of this terminology may be freely copied and distributed by users. IFAA member societies are authorized to publish translations of this terminology. Authors of other works that might be considered derivative should write to the Chair of FIPAT for permission to publish a derivative work. Caput V: ORGANOGENESIS Chapter 5: ORGANOGENESIS
    [Show full text]
  • Sightsavers Policy on Recycled Spectacles
    DRAFT POSITION PAPER ADJUSTABLE SPECTACLES Position statement There are an estimated 670 million cases of blindness or vision impairment (153 million people with impaired far visioni and 517 million people with impaired near visionii) simply because they are unable to access an appropriate eye examination and spectacles. Far vision impairment alone costs $269billion a year in lost productivity.iii The massive volume of cases, and consequent scale of disability and economic impact caused by uncorrected refractive error (URE) has lead to various attempts to provide short-cut refractive care. Adjustable spectacles, with the optical power either set in an eye examination or self-adjusted, have been promoted by several companies and organizations as a potential solution.iv IAPB recognises the good intentions behind these short-cuts and spectacle technology but advises that its members and other parties engaged in promoting eye health should exercise caution with or avoid adjustable spectacles at this time. In deciding whether and how to use adjustable spectacles in future, the following areas should be considered. Considerations Sustainability It is critical that refractive services are provided in a manner that contributes to affordable, high quality eye care for all patients irrespective of social standing. Isolated provision of spectacles is detrimental to the human resources and service delivery systems that are necessary for sustainable eye care services, and so should be avoided whenever possible. • Adjustable spectacles that are affordable, comfortable, cosmetically acceptable and optically accurate may have a role contributing to sustainability when used by trained personnel within the recognised service delivery system of the jurisdiction • Adjustable spectacles used in a way (e.g.
    [Show full text]
  • Introduction the Human
    Physics 1CL ·OPTICAL INSTRUMENTS AND THE EYE SPRING 2010 Introduction Most of the subject material in this lab can be found in Chapter 25 of Serway and Faughn. In this lab, you will make images of images using lenses and the optical bench (Experiment A). IT IS IMPERATIVE THAT YOU READ CHAPTER 25 BEFORE COMING TO LAB! You will study your own eye as an optical instrument and measure the distance on your retina from the fovea to the “blind spot” (Experiment B). You will also study a model of the eye, and examine the ability of the lens to bring an object into focus at different distances. You will examine how an abnormal eyeball causes blurred vision and how to correct this (Experiment C). There is only one station with the model of the human eye. Whenever that station becomes available, take a few minutes at that station to perform Experiment C. The Human Eye The figure shows a cross section of a human eye. Light is refracted at the surface of the cornea, and is refracted again as it passes through the “crystalline” lens. In a normal eye, light is perfectly focused on the receptors in the retina where signals are generated in nerve fibers and transmitted to the brain. An inverted image is formed on the retina, but the brain “expects” this as normal and is wired to recognize this as normal. Unless you are studying details of the function of the eye, we can consider it to be a single lens (where the focal length can be varied), and a fixed distance from the lens to the retina where we would prefer to make sharply focused images.
    [Show full text]
  • Considering Contact Lens CORNEAL RESHAPING
    Considering Contact Lens CORNEAL RESHAPING Patient Information Booklet for Potential Users of PARAGON RG-4 Contact Lens Corneal Reshaping PATIENT INFORMATION BOOKLET FOR POTENTIAL USERS OF PARAGON RG-4 Manufactured in Paragon HDS® 100 (paflufocon D) Contact Lenses For Contact Lens Corneal Reshaping Overnight Wear CAUTION: Federal (US) law restricts this device to sale by, or on the order of a licensed practitioner. Contact lenses for corneal reshaping should be fitted only by a trained and certified contact lens fitter. Nonsterile. Clean and condition lenses prior to use. ii TABLE OF CONTENTS Page Introduction 1 How The Eye Functions 1 How Paragon RG-4 Contact Lenses For Corneal Reshaping Function 2 Alternative Ways To Correct Nearsightedness 3 Risk Analysis 3 Indications 4 Precautions 4 Contraindications (Reasons Not To Use) 6 Warnings 6 Adverse Effects (Problems and What To Do) 7 Clinical Study Data 7 Overnight Wear Safety Summary 12 Maintaining Effects of Paragon RG-4 Lenses For Corneal Reshaping 13 Glossary 14 iii INTRODUCTION The information in this booklet is to help you decide whether or not to be fitted with Paragon RG-4 lens designs for Contact Lens Corneal Reshaping. Corneal reshaping is a fitting procedure that temporarily corrects or greatly reduces nearsightedness (known by the medical name, myopia) with or without astigmatism after contact lenses have been removed. By temporary, it is meant that the contact lenses are worn while sleeping (overnight) and then removed upon awaking; whereupon the nearsightedness remains corrected or greatly reduced for all or most of your waking hours. The exact time period over which the myopia remains corrected varies with each patient.
    [Show full text]
  • To See the Invisible: the Quest of Imaging Vitreous J
    DOP42005.qxd 4/15/08 11:34 AM Page 5 Meyer CH (ed): Vital Dyes in Vitreoretinal Surgery. Dev Ophthalmol. Basel, Karger, 2008, vol 42, pp 5–28 To See the Invisible: The Quest of Imaging Vitreous J. Sebag VMR Institute, University of Southern California, Los Angeles, Calif., USA Abstract Purpose: Imaging vitreous has long been a quest to view what is, by design, invisible. This chapter will review important historical aspects, past and present imaging methodologies, and new technologies that are currently in development for future research and clinical applications. Methods: Classic and modern histologic techniques, dark-field slit microscopy, clinical slit lamp biomicroscopy, standard and scanning laser ophthalmoscopy (SLO), ultrasonography, optical coherence tomography (OCT), com- bined OCT-SLO, magnetic resonance and Raman spectroscopies, and dynamic light scattering method- ologies are presented. Results: The best available histologic techniques for imaging vitreous are those that avoid rapid dehydration of vitreous specimens. Dark-field slit microscopy enables in vitro imaging without dehydration or tissue fixatives. OCT enables better in vivo visualization of the vitreoretinal inter- face than SLO and ultrasonography, but does not adequately image the vitreous body. The combination of OCT with SLO has provided useful new imaging capabilities, but only at the vitreoretinal interface. Dynamic light scattering can evaluate the vitreous body by determining the average sizes of vitreous macromolecules in aging, disease, and as a means to assess the effects of pharmacologic vitreolysis. Raman spectroscopy can detect altered vitreous molecules, such as glycated collagen and other pro- teins in diabetic vitreopathy and possibly other diseases. Conclusions: A better understanding of normal vitreous physiology and structure and how these change in aging and disease is needed to develop more effective therapies and prevention.
    [Show full text]
  • Relationship Between Lenticular Power and Refractive Error in Children with Hyperopia
    Clinical Ophthalmology Dovepress open access to scientific and medical research Open Access Full Text Article ORIGINAL RESEARCH Relationship between lenticular power and refractive error in children with hyperopia Takeshi Tomomatsu Objectives: To evaluate the contribution of axial length, and lenticular and corneal power to Shinjiro Kono the spherical equivalent refractive error in children with hyperopia between 3 and 13 years of Shogo Arimura age, using noncontact optical biometry. Yoko Tomomatsu Methods: There were 62 children between 3 and 13 years of age with hyperopia (+2 diopters Takehiro Matsumura [D] or more) who underwent automated refraction measurement with cycloplegia, to measure Yuji Takihara spherical equivalent refractive error and corneal power. Axial length was measured using an optic biometer that does not require contact with the cornea. The refractive power of the lens Masaru Inatani was calculated using the Sanders-Retzlaff-Kraff formula. Single regression analysis was used Yoshihiro Takamura to evaluate the correlation among the optical parameters. For personal use only. Department of Ophthalmology, Results: There was a significant positive correlation between age and axial length P( = 0.0014); Faculty of Medical Sciences, University of Fukui, Fukuiken, Japan however, the degree of hyperopia did not decrease with aging (P = 0.59). There was a significant negative correlation between age and the refractive power of the lens (P = 0.0001) but not that of the cornea (P = 0.43). A significant negative correlation was observed between the degree of hyperopia and lenticular power (P , 0.0001). Conclusion: Although this study is small scale and cross sectional, the analysis, using noncontact biometry, showed that lenticular power was negatively correlated with refractive error and age, indicating that lower lens power may contribute to the degree of hyperopia.
    [Show full text]
  • Nomina Histologica Veterinaria, First Edition
    NOMINA HISTOLOGICA VETERINARIA Submitted by the International Committee on Veterinary Histological Nomenclature (ICVHN) to the World Association of Veterinary Anatomists Published on the website of the World Association of Veterinary Anatomists www.wava-amav.org 2017 CONTENTS Introduction i Principles of term construction in N.H.V. iii Cytologia – Cytology 1 Textus epithelialis – Epithelial tissue 10 Textus connectivus – Connective tissue 13 Sanguis et Lympha – Blood and Lymph 17 Textus muscularis – Muscle tissue 19 Textus nervosus – Nerve tissue 20 Splanchnologia – Viscera 23 Systema digestorium – Digestive system 24 Systema respiratorium – Respiratory system 32 Systema urinarium – Urinary system 35 Organa genitalia masculina – Male genital system 38 Organa genitalia feminina – Female genital system 42 Systema endocrinum – Endocrine system 45 Systema cardiovasculare et lymphaticum [Angiologia] – Cardiovascular and lymphatic system 47 Systema nervosum – Nervous system 52 Receptores sensorii et Organa sensuum – Sensory receptors and Sense organs 58 Integumentum – Integument 64 INTRODUCTION The preparations leading to the publication of the present first edition of the Nomina Histologica Veterinaria has a long history spanning more than 50 years. Under the auspices of the World Association of Veterinary Anatomists (W.A.V.A.), the International Committee on Veterinary Anatomical Nomenclature (I.C.V.A.N.) appointed in Giessen, 1965, a Subcommittee on Histology and Embryology which started a working relation with the Subcommittee on Histology of the former International Anatomical Nomenclature Committee. In Mexico City, 1971, this Subcommittee presented a document entitled Nomina Histologica Veterinaria: A Working Draft as a basis for the continued work of the newly-appointed Subcommittee on Histological Nomenclature. This resulted in the editing of the Nomina Histologica Veterinaria: A Working Draft II (Toulouse, 1974), followed by preparations for publication of a Nomina Histologica Veterinaria.
    [Show full text]
  • Topic 3: Operation of Simple Lens
    V N I E R U S E I T H Y Modern Optics T O H F G E R D I N B U Topic 3: Operation of Simple Lens Aim: Covers imaging of simple lens using Fresnel Diffraction, resolu- tion limits and basics of aberrations theory. Contents: 1. Phase and Pupil Functions of a lens 2. Image of Axial Point 3. Example of Round Lens 4. Diffraction limit of lens 5. Defocus 6. The Strehl Limit 7. Other Aberrations PTIC D O S G IE R L O P U P P A D E S C P I A S Properties of a Lens -1- Autumn Term R Y TM H ENT of P V N I E R U S E I T H Y Modern Optics T O H F G E R D I N B U Ray Model Simple Ray Optics gives f Image Object u v Imaging properties of 1 1 1 + = u v f The focal length is given by 1 1 1 = (n − 1) + f R1 R2 For Infinite object Phase Shift Ray Optics gives Delta Fn f Lens introduces a path length difference, or PHASE SHIFT. PTIC D O S G IE R L O P U P P A D E S C P I A S Properties of a Lens -2- Autumn Term R Y TM H ENT of P V N I E R U S E I T H Y Modern Optics T O H F G E R D I N B U Phase Function of a Lens δ1 δ2 h R2 R1 n P0 P ∆ 1 With NO lens, Phase Shift between , P0 ! P1 is 2p F = kD where k = l with lens in place, at distance h from optical, F = k0d1 + d2 +n(D − d1 − d2)1 Air Glass @ A which can be arranged to|giv{ze } | {z } F = knD − k(n − 1)(d1 + d2) where d1 and d2 depend on h, the ray height.
    [Show full text]
  • I. Multiple Mechanisms of Accommodation A. Variable Axial Length B
    Mechanics, Aging and Neurological Control of accommodation: I. Multiple Mechanisms of Accommodation A. Variable axial length B. Corneal Power C. Lenticular power D. Pupil size E. Lenticular refractive index gradient (isoindical surfaces) II. Anatomy A. Lens B. Capsule C. Zonules D. Ciliary Body E. Index gradient III. Autonomic innervation IV. Amplitude of accommodation and age A. Functional presbyopia B. Absolute presbyopia C. Treatment Bifocals Monovision Surgically implanted prosthesis Course title - (VS217) Oculomotor functions and neurology Instructor - Clifton Schor GSI: James O’Shea, Michael Oliver & Aleks Polosukhina Schedule of lectures, exams and laboratories : Lecture hours 10-11:30 Tu Th; 5 min break at 11:00 Labs Friday the first 3 weeks Examination Schedule : Quizes: January 29; February 28 Midterm: February 14: Final March 13 Power point lecture slides are available on a CD Resources: text books, reader , website, handouts Class Website: Reader. Website http://schorlab.berkeley.edu Click courses 117 class page name VS117 password Hering,1 First Week: read chapters 16-18 See lecture outline in syllabus Labs begin this Friday, January 25 Course Goals Near Response - Current developments in optometry Myopia control – environmental, surgical, pharmaceutical and genetic Presbyopia treatment – amelioration and prosthetic treatment Developmental disorders (amblyopia and strabismus) Reading disorders Ergonomics- computers and sports vision Virtual reality and personal computer eye-ware Neurology screening- Primary care gate keeper neurology, systemic, endocrines, metabolic, muscular skeletal systems. Mechanics, Aging and Neurological Control of accommodation : I. Five Mechanisms of Accommodation A. Variable axial length B. Corneal Power and astigmatism C. Lenticular power D. Pupil size & Aberrations E. Lenticular refractive index gradient (isoindical surfaces) II.
    [Show full text]
  • The Camera Versus the Human Eye
    The Camera Versus the Human Eye Nov 17, 2012 ∙ Roger Cicala This article was originally published as a blog. Permission was granted by Roger Cicala to re‐ publish the article on the CTI website. It is an excellent article for those police departments considering the use of cameras. This article started after I followed an online discussion about whether a 35mm or a 50mm lens on a full frame camera gives the equivalent field of view to normal human vision. This particular discussion immediately delved into the optical physics of the eye as a camera and lens — an understandable comparison since the eye consists of a front element (the cornea), an aperture ring (the iris and pupil), a lens, and a sensor (the retina). Despite all the impressive mathematics thrown back and forth regarding the optical physics of the eyeball, the discussion didn’t quite seem to make sense logically, so I did a lot of reading of my own on the topic. There won’t be any direct benefit from this article that will let you run out and take better photographs, but you might find it interesting. You may also find it incredibly boring, so I’ll give you my conclusion first, in the form of two quotes from Garry Winogrand: A photograph is the illusion of a literal description of how the camera ‘saw’ a piece of time and space. Photography is not about the thing photographed. It is about how that thing looks photographed. Basically in doing all this research about how the human eye is like a camera, what I really learned is how human vision is not like a photograph.
    [Show full text]
  • 6. Refractive Errors .Pdf
    Refractive Errors Objectives: ● Not given. [ Color index : Important | Notes | Extra ] ​ ​ ​ ​ ​ ​ ​ Resources: Slides+Notes+Lecture notes of ophthalmology+434team. ​ Done by : Abdulrahman Al-Shammari & Munira alhussaini ​ Edited by: Munerah alOmari ​ Revised by : Adel Al Shihri, Lina Alshehri. ​ FACTS: ● 75% of avoidable blindness is due to: ● Uncorrected refractive error ● Cataract ● Trachoma Physiology: ● To have a clear picture in the retina & to be seen in the brain, there should be a clear cornea, clear anterior chamber, and clear lens, clear vitreous cavity then the picture should be focused on the retina with normal refractive index. ● The retina is responsible for the perception of light. It converts light rays into impulses; sent through the optic nerve to your brain, where they are recognized as images. ● Normal refractive power of the eye is 60 diopters. (The cornea accounts for approximately two-thirds ​ ​ ​ ​ .(and the crystalline lens contributes the remaining (ﺛﺎﺑﺖ of this refractive power (about 40 diopters 60 is the power when we’re looking at something far ( the lens is relaxed). but when we look at near objects the lens’s power increases according to the distance of the object we’re looking at. ● The normal axial length is 22.5 mml (it’s measured from the tip of the cornea to the surface of the ​ ​ ​ ​ retina). ● If the axial length is longer = the picture will be in front of the retina “Myopia”. ​ ​ ​ ​ ​ ​ ● If the axial length is shorter = the picture will be behind the retina “Hyperopia”. ​ ​ ​ ​ ​ ​ ​ ❖Refraction: ● In optics, refraction occurs when light waves travel from a medium with a given refractive index to a medium with another.
    [Show full text]
  • Behavioral Optometric Science Student Manual
    Pacific University CommonKnowledge College of Optometry Theses, Dissertations and Capstone Projects 9-2004 Behavioral optometric science student manual Kristel Rogers Pacific University Recommended Citation Rogers, Kristel, "Behavioral optometric science student manual" (2004). College of Optometry. 1486. https://commons.pacificu.edu/opt/1486 This Thesis is brought to you for free and open access by the Theses, Dissertations and Capstone Projects at CommonKnowledge. It has been accepted for inclusion in College of Optometry by an authorized administrator of CommonKnowledge. For more information, please contact [email protected]. Behavioral optometric science student manual Abstract Purpose: To provide the first year optometry student with a simplified guide to behavioral optometry terminology and concepts. The goal is for the student to gain a better understanding of behavioral optometry throughout the first semester. Methods: The coursework from Optometry 562 has been broken into four sections. Each author has written about one of these sections in her own perspective as another way to explain behavioral optometry. This publication is one of the four sections written. It covers types of refractive conditions, their etiology, and how to compensate for them. It also includes affects of stress on vision and theories on adaptation to visual stress both short-term and long-term. Lastly, classification and etiology of myopia is discussed to better understand this common refractive condition. Other Authors of Manual: Angela Darveaux, Katherine Chhor, Kim Schweiger Degree Type Thesis Degree Name Master of Science in Vision Science Committee Chair Bradley Coffey Subject Categories Optometry This thesis is available at CommonKnowledge: https://commons.pacificu.edu/opt/1486 Copyright and terms of use If you have downloaded this document directly from the web or from CommonKnowledge, see the “Rights” section on the previous page for the terms of use.
    [Show full text]