Lecture 5 - Vision Physiology | Animal Physiology and Functional Histology- I - MBBS PDF Download

 Page 1


Physiology of Vision 
 
              Institute of Life Long Learning, University of Delhi  
 
1 
 
 
 
 
 
 
Zoology 
Lesson: Physiology of Vision 
Lesson Developer: Dr. Mahtab Zarin 
College/Dept: Zoology, University of Delhi 
  
 
 
 
 
 
 
 
 
 
 
 
 
Page 2


Physiology of Vision 
 
              Institute of Life Long Learning, University of Delhi  
 
1 
 
 
 
 
 
 
Zoology 
Lesson: Physiology of Vision 
Lesson Developer: Dr. Mahtab Zarin 
College/Dept: Zoology, University of Delhi 
  
 
 
 
 
 
 
 
 
 
 
 
 
Physiology of Vision 
 
              Institute of Life Long Learning, University of Delhi  
 
2 
 
Table of Contents 
? Introduction 
? Image formation mechanisms  
? Refraction of light rays 
? Accommodation 
? Change in pupil size 
? Types of vision 
? Errors of refraction 
? Photochemistry of vision 
? Rhodopsin-retinal visual cycle and excitation of rods 
? Processing and transmission of visual impulse  
? Visual perception 
? Summary 
? Exercises 
? Glossary 
? References 
 
 
 
 
 
 
 
 
 
Page 3


Physiology of Vision 
 
              Institute of Life Long Learning, University of Delhi  
 
1 
 
 
 
 
 
 
Zoology 
Lesson: Physiology of Vision 
Lesson Developer: Dr. Mahtab Zarin 
College/Dept: Zoology, University of Delhi 
  
 
 
 
 
 
 
 
 
 
 
 
 
Physiology of Vision 
 
              Institute of Life Long Learning, University of Delhi  
 
2 
 
Table of Contents 
? Introduction 
? Image formation mechanisms  
? Refraction of light rays 
? Accommodation 
? Change in pupil size 
? Types of vision 
? Errors of refraction 
? Photochemistry of vision 
? Rhodopsin-retinal visual cycle and excitation of rods 
? Processing and transmission of visual impulse  
? Visual perception 
? Summary 
? Exercises 
? Glossary 
? References 
 
 
 
 
 
 
 
 
 
Physiology of Vision 
 
              Institute of Life Long Learning, University of Delhi  
 
3 
 
Learning objectives 
? To describe the structure of eyes as a photoreception organ 
? Pathways of Visual information from eye to brain 
? To understand the mechanisms of image formations 
? Role of the photoreceptors in image processing 
? Refraction of the light rays on cornea  
? To understand the visual perception of the object  
 
Introduction 
Vision is the special sense of sight that is based on the transduction of light stimuli received 
through the eyes.  Each eye with layer of receptors, lens system, and nerves act as sensory 
receptor for vision.  
Receptors of the eyes are able to detect a small portion of the vast spectrum of the 
electromagnetic radiation that we call visible light (Fig. 5). The wavelengths capable of 
stimulating the receptors of the eye-visible spectrum- are between about 400 and 700nm. 
Different wavelengths of light within band are perceived as different colors. 
Page 4


Physiology of Vision 
 
              Institute of Life Long Learning, University of Delhi  
 
1 
 
 
 
 
 
 
Zoology 
Lesson: Physiology of Vision 
Lesson Developer: Dr. Mahtab Zarin 
College/Dept: Zoology, University of Delhi 
  
 
 
 
 
 
 
 
 
 
 
 
 
Physiology of Vision 
 
              Institute of Life Long Learning, University of Delhi  
 
2 
 
Table of Contents 
? Introduction 
? Image formation mechanisms  
? Refraction of light rays 
? Accommodation 
? Change in pupil size 
? Types of vision 
? Errors of refraction 
? Photochemistry of vision 
? Rhodopsin-retinal visual cycle and excitation of rods 
? Processing and transmission of visual impulse  
? Visual perception 
? Summary 
? Exercises 
? Glossary 
? References 
 
 
 
 
 
 
 
 
 
Physiology of Vision 
 
              Institute of Life Long Learning, University of Delhi  
 
3 
 
Learning objectives 
? To describe the structure of eyes as a photoreception organ 
? Pathways of Visual information from eye to brain 
? To understand the mechanisms of image formations 
? Role of the photoreceptors in image processing 
? Refraction of the light rays on cornea  
? To understand the visual perception of the object  
 
Introduction 
Vision is the special sense of sight that is based on the transduction of light stimuli received 
through the eyes.  Each eye with layer of receptors, lens system, and nerves act as sensory 
receptor for vision.  
Receptors of the eyes are able to detect a small portion of the vast spectrum of the 
electromagnetic radiation that we call visible light (Fig. 5). The wavelengths capable of 
stimulating the receptors of the eye-visible spectrum- are between about 400 and 700nm. 
Different wavelengths of light within band are perceived as different colors. 
Physiology of Vision 
 
              Institute of Life Long Learning, University of Delhi  
 
4 
 
Fig. 1. Electromagnetic spectrum 
Visible light ranges in wavelength from 400 to 700nm. 
Source: http://en.wikipedia.org/wiki/File:EM_spectrum.svg  
Image Credit: This file is licensed under the Creative Commons Attribution ShareAlike 3.0 License. 
Value addition: Did you Know  
Color of Object depends on the wavelength reflected 
An object can absorb certain wavelengths of visible light and reflect others; the 
object will appear the color of wavelength that is reflected. For example,  
? A green apple appears green because it reflects mostly green light and absorbs 
most other wavelengths of visible light.   
? An object appears white because it reflects all wavelength of visible light.  
? An object appears black because it absorbs all wavelength of visible light.  
Source: Principles of Anatomy & Physiology- Tortora, G.J. & Derrickson, B.  
 
Image formation mechanisms  
Page 5


Physiology of Vision 
 
              Institute of Life Long Learning, University of Delhi  
 
1 
 
 
 
 
 
 
Zoology 
Lesson: Physiology of Vision 
Lesson Developer: Dr. Mahtab Zarin 
College/Dept: Zoology, University of Delhi 
  
 
 
 
 
 
 
 
 
 
 
 
 
Physiology of Vision 
 
              Institute of Life Long Learning, University of Delhi  
 
2 
 
Table of Contents 
? Introduction 
? Image formation mechanisms  
? Refraction of light rays 
? Accommodation 
? Change in pupil size 
? Types of vision 
? Errors of refraction 
? Photochemistry of vision 
? Rhodopsin-retinal visual cycle and excitation of rods 
? Processing and transmission of visual impulse  
? Visual perception 
? Summary 
? Exercises 
? Glossary 
? References 
 
 
 
 
 
 
 
 
 
Physiology of Vision 
 
              Institute of Life Long Learning, University of Delhi  
 
3 
 
Learning objectives 
? To describe the structure of eyes as a photoreception organ 
? Pathways of Visual information from eye to brain 
? To understand the mechanisms of image formations 
? Role of the photoreceptors in image processing 
? Refraction of the light rays on cornea  
? To understand the visual perception of the object  
 
Introduction 
Vision is the special sense of sight that is based on the transduction of light stimuli received 
through the eyes.  Each eye with layer of receptors, lens system, and nerves act as sensory 
receptor for vision.  
Receptors of the eyes are able to detect a small portion of the vast spectrum of the 
electromagnetic radiation that we call visible light (Fig. 5). The wavelengths capable of 
stimulating the receptors of the eye-visible spectrum- are between about 400 and 700nm. 
Different wavelengths of light within band are perceived as different colors. 
Physiology of Vision 
 
              Institute of Life Long Learning, University of Delhi  
 
4 
 
Fig. 1. Electromagnetic spectrum 
Visible light ranges in wavelength from 400 to 700nm. 
Source: http://en.wikipedia.org/wiki/File:EM_spectrum.svg  
Image Credit: This file is licensed under the Creative Commons Attribution ShareAlike 3.0 License. 
Value addition: Did you Know  
Color of Object depends on the wavelength reflected 
An object can absorb certain wavelengths of visible light and reflect others; the 
object will appear the color of wavelength that is reflected. For example,  
? A green apple appears green because it reflects mostly green light and absorbs 
most other wavelengths of visible light.   
? An object appears white because it reflects all wavelength of visible light.  
? An object appears black because it absorbs all wavelength of visible light.  
Source: Principles of Anatomy & Physiology- Tortora, G.J. & Derrickson, B.  
 
Image formation mechanisms  
Physiology of Vision 
 
              Institute of Life Long Learning, University of Delhi  
 
5 
To create clear vision, light reflected from objects within the visual field is focused on to the 
retina of each eye. The followings are the steps implicated in achieving a clear image:   
1. the Refraction or bending of light through lens and cornea in eye; 
2. Accommodation, the adjustment in shape of the lens; 
3. Changing the size of the pupils, Constriction or narrowing  
 
Refraction of light rays 
Refraction is of light rays is bending of the rays at an angulated interface. It is a 
phenomenon that often occurs when light rays travel from a medium with a given refractive 
index to a medium with another at an oblique angle. At the boundary between the media, 
the wave's phase velocity is altered, usually causing a change in direction. Its wavelength 
increases or decreases but its frequency remains constant. The degree of refraction 
increases as a function of 
i) ratio of the two refractive indices of the two transparent media 
ii) degree of angulation between the interface and the entering wave front. 
Refractive index can be defined as the ratio of velocity of light in air to the velocity in a 
substance. 
 Human eye is optically equivalent to a camera which has a lens system, a variable aperture 
in form of pupil and a retina which corresponds to photographic film. 
Lens system of the eye has four refractive interfaces between: 
a) air and anterior surface of cornea 
b) posterior of camera and aqueous humor 
c) aqueous humor and anterior surface of lens 
d) posterior surface of lens and vitreous humor. 
The refractive index of air is 1.00, cornea-1.38, aqueous humor-1.33, lens-1.40 and 
vitreous humor-1.34.