Lecture 4 - Structure of eye | Animal Physiology and Functional Histology- I - MBBS PDF Download

 Page 1


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


Structure of Eye 
 
              Institute of Life Long Learning, University of Delhi  
 
1 
 
 
 
 
 
 
 
Zoology 
Lesson: Structure of eye 
Lesson Developer: Dr. Mahtab Zarin 
College/Dept: Zoology, University of Delhi 
 
 
 
 
 
 
 
 
 
 
 
Structure of Eye 
 
              Institute of Life Long Learning, University of Delhi  
 
2 
 
Table of Contents 
? Introduction 
? Structure of the eyeball 
? Outer fibrous layer 
? Cornea 
? Sclera 
? Middle vascular layer 
? Choroid 
? Ciliary body 
? Iris 
? Inner layer or Retina 
? Rods and cones 
? Photo pigments 
? Optic nerve 
? Lens  
? Interior of the eyeball 
? Eye movements 
? Accessory organs of the eye 
? Summary 
? Exercises 
? Glossary 
? References 
 
 
 
 
Page 3


Structure of Eye 
 
              Institute of Life Long Learning, University of Delhi  
 
1 
 
 
 
 
 
 
 
Zoology 
Lesson: Structure of eye 
Lesson Developer: Dr. Mahtab Zarin 
College/Dept: Zoology, University of Delhi 
 
 
 
 
 
 
 
 
 
 
 
Structure of Eye 
 
              Institute of Life Long Learning, University of Delhi  
 
2 
 
Table of Contents 
? Introduction 
? Structure of the eyeball 
? Outer fibrous layer 
? Cornea 
? Sclera 
? Middle vascular layer 
? Choroid 
? Ciliary body 
? Iris 
? Inner layer or Retina 
? Rods and cones 
? Photo pigments 
? Optic nerve 
? Lens  
? Interior of the eyeball 
? Eye movements 
? Accessory organs of the eye 
? Summary 
? Exercises 
? Glossary 
? References 
 
 
 
 
Structure of Eye 
 
              Institute of Life Long Learning, University of Delhi  
 
3 
 
 
Learning objectives 
? To describe the structure of eyes as a photoreception organ 
? Structural and functional parts of the eyes 
? Functions of  extraocular eye muscles 
? The structure and role of accessory part in eye protection 
 
Introduction 
Vision, the act of seeing, is extremely important to survival of animal. Our eyes are intricate 
organs of sense in order to see the thing around us. The human eye has been known to 
evolve from ancient light-sensitive spots in invertebrates. Enclosed within its protective 
layering, each eye consists of layer of receptors, lens system, and a nervous system. 
Interestingly, more than half the sensory receptors in the human body are positioned in the 
eyes and a great part of the cerebral cortex is devoted to process visual information. In 
brief, lens system focuses light on the receptors and nerves system conduct impulses from 
the receptors to the brain. Physiological aspects of eye or vision will be explained in detailed 
in following sections and subsections. 
 Structure of Eye (Fig. 1) 
The eyes are located within either orbit in the skull which surrounds the eyeballs, protecting 
them and anchoring the soft tissues of the eye. The eyelids, with lashes at their leading 
edges protect the eye from abrasions by blocking particles entering the surface of the eye.  
 
The eye is formed by three layers, or tunics that form the optic and photoreceptive 
apparatus of the eye. Each of these three layers has structural and nutritive functions and 
parts. From the outside to the inside of the eyeball the three tunics are as follows:  
1. Fibrous tunic or Outer fibrous layer 
? Forms a capsule enclosing and protecting the other components of the eye.  
? Can be subdivided into the sclera, with primarily structural functions, and the cornea, 
which is part of the optic apparatus. 
2. Vascular tunic /Middle vascular layer  
Page 4


Structure of Eye 
 
              Institute of Life Long Learning, University of Delhi  
 
1 
 
 
 
 
 
 
 
Zoology 
Lesson: Structure of eye 
Lesson Developer: Dr. Mahtab Zarin 
College/Dept: Zoology, University of Delhi 
 
 
 
 
 
 
 
 
 
 
 
Structure of Eye 
 
              Institute of Life Long Learning, University of Delhi  
 
2 
 
Table of Contents 
? Introduction 
? Structure of the eyeball 
? Outer fibrous layer 
? Cornea 
? Sclera 
? Middle vascular layer 
? Choroid 
? Ciliary body 
? Iris 
? Inner layer or Retina 
? Rods and cones 
? Photo pigments 
? Optic nerve 
? Lens  
? Interior of the eyeball 
? Eye movements 
? Accessory organs of the eye 
? Summary 
? Exercises 
? Glossary 
? References 
 
 
 
 
Structure of Eye 
 
              Institute of Life Long Learning, University of Delhi  
 
3 
 
 
Learning objectives 
? To describe the structure of eyes as a photoreception organ 
? Structural and functional parts of the eyes 
? Functions of  extraocular eye muscles 
? The structure and role of accessory part in eye protection 
 
Introduction 
Vision, the act of seeing, is extremely important to survival of animal. Our eyes are intricate 
organs of sense in order to see the thing around us. The human eye has been known to 
evolve from ancient light-sensitive spots in invertebrates. Enclosed within its protective 
layering, each eye consists of layer of receptors, lens system, and a nervous system. 
Interestingly, more than half the sensory receptors in the human body are positioned in the 
eyes and a great part of the cerebral cortex is devoted to process visual information. In 
brief, lens system focuses light on the receptors and nerves system conduct impulses from 
the receptors to the brain. Physiological aspects of eye or vision will be explained in detailed 
in following sections and subsections. 
 Structure of Eye (Fig. 1) 
The eyes are located within either orbit in the skull which surrounds the eyeballs, protecting 
them and anchoring the soft tissues of the eye. The eyelids, with lashes at their leading 
edges protect the eye from abrasions by blocking particles entering the surface of the eye.  
 
The eye is formed by three layers, or tunics that form the optic and photoreceptive 
apparatus of the eye. Each of these three layers has structural and nutritive functions and 
parts. From the outside to the inside of the eyeball the three tunics are as follows:  
1. Fibrous tunic or Outer fibrous layer 
? Forms a capsule enclosing and protecting the other components of the eye.  
? Can be subdivided into the sclera, with primarily structural functions, and the cornea, 
which is part of the optic apparatus. 
2. Vascular tunic /Middle vascular layer  
Structure of Eye 
 
              Institute of Life Long Learning, University of Delhi  
 
4 
? Tunic is also called the uveal tract. 
? Can be divided into choroid, ciliary body and iris.  
? The choroid has primarily nutritive functions.  
? The ciliary body generates the aqueous humor of the eye and the ciliary muscle 
functions in the optic apparatus.  
? The iris as part of the optic apparatus acts as a contractile diaphragm, i.e. the 
aperture of the eye.  
3. Neural tunic /Inner layer  
? Consists of the retina which gets its circulation from the vessels of the choroid as 
well as the retinal vessels.  
? The retina proper forms the photoreceptive layer of the eye.  
? As a double-layered epithelium, the retina also covers the ciliary process and the 
posterior surface of the iris, where it has both nutritive and structural functions. 
 
Within these coats are the aqueous humour, the vitreous body, and the flexible lens. 
The aqueous humour is a clear fluid that is contained in two areas: the anterior chamber 
between the cornea and the iris, and the posterior chamber between the iris and the lens. 
The lens is suspended to the ciliary body by the suspensory ligament (Zonule of Zinn), 
made up of fine transparent fibers.  
The vitreous body is a clear jelly that is much larger than the aqueous humour present 
behind the lens, and the rest is bordered by the sclera, zonule, and lens. They are connected 
via the pupil 
 
 
 
 
Page 5


Structure of Eye 
 
              Institute of Life Long Learning, University of Delhi  
 
1 
 
 
 
 
 
 
 
Zoology 
Lesson: Structure of eye 
Lesson Developer: Dr. Mahtab Zarin 
College/Dept: Zoology, University of Delhi 
 
 
 
 
 
 
 
 
 
 
 
Structure of Eye 
 
              Institute of Life Long Learning, University of Delhi  
 
2 
 
Table of Contents 
? Introduction 
? Structure of the eyeball 
? Outer fibrous layer 
? Cornea 
? Sclera 
? Middle vascular layer 
? Choroid 
? Ciliary body 
? Iris 
? Inner layer or Retina 
? Rods and cones 
? Photo pigments 
? Optic nerve 
? Lens  
? Interior of the eyeball 
? Eye movements 
? Accessory organs of the eye 
? Summary 
? Exercises 
? Glossary 
? References 
 
 
 
 
Structure of Eye 
 
              Institute of Life Long Learning, University of Delhi  
 
3 
 
 
Learning objectives 
? To describe the structure of eyes as a photoreception organ 
? Structural and functional parts of the eyes 
? Functions of  extraocular eye muscles 
? The structure and role of accessory part in eye protection 
 
Introduction 
Vision, the act of seeing, is extremely important to survival of animal. Our eyes are intricate 
organs of sense in order to see the thing around us. The human eye has been known to 
evolve from ancient light-sensitive spots in invertebrates. Enclosed within its protective 
layering, each eye consists of layer of receptors, lens system, and a nervous system. 
Interestingly, more than half the sensory receptors in the human body are positioned in the 
eyes and a great part of the cerebral cortex is devoted to process visual information. In 
brief, lens system focuses light on the receptors and nerves system conduct impulses from 
the receptors to the brain. Physiological aspects of eye or vision will be explained in detailed 
in following sections and subsections. 
 Structure of Eye (Fig. 1) 
The eyes are located within either orbit in the skull which surrounds the eyeballs, protecting 
them and anchoring the soft tissues of the eye. The eyelids, with lashes at their leading 
edges protect the eye from abrasions by blocking particles entering the surface of the eye.  
 
The eye is formed by three layers, or tunics that form the optic and photoreceptive 
apparatus of the eye. Each of these three layers has structural and nutritive functions and 
parts. From the outside to the inside of the eyeball the three tunics are as follows:  
1. Fibrous tunic or Outer fibrous layer 
? Forms a capsule enclosing and protecting the other components of the eye.  
? Can be subdivided into the sclera, with primarily structural functions, and the cornea, 
which is part of the optic apparatus. 
2. Vascular tunic /Middle vascular layer  
Structure of Eye 
 
              Institute of Life Long Learning, University of Delhi  
 
4 
? Tunic is also called the uveal tract. 
? Can be divided into choroid, ciliary body and iris.  
? The choroid has primarily nutritive functions.  
? The ciliary body generates the aqueous humor of the eye and the ciliary muscle 
functions in the optic apparatus.  
? The iris as part of the optic apparatus acts as a contractile diaphragm, i.e. the 
aperture of the eye.  
3. Neural tunic /Inner layer  
? Consists of the retina which gets its circulation from the vessels of the choroid as 
well as the retinal vessels.  
? The retina proper forms the photoreceptive layer of the eye.  
? As a double-layered epithelium, the retina also covers the ciliary process and the 
posterior surface of the iris, where it has both nutritive and structural functions. 
 
Within these coats are the aqueous humour, the vitreous body, and the flexible lens. 
The aqueous humour is a clear fluid that is contained in two areas: the anterior chamber 
between the cornea and the iris, and the posterior chamber between the iris and the lens. 
The lens is suspended to the ciliary body by the suspensory ligament (Zonule of Zinn), 
made up of fine transparent fibers.  
The vitreous body is a clear jelly that is much larger than the aqueous humour present 
behind the lens, and the rest is bordered by the sclera, zonule, and lens. They are connected 
via the pupil 
 
 
 
 
Structure of Eye 
 
              Institute of Life Long Learning, University of Delhi  
 
5 
Fig. 1. Structures of Eyeball 
Source: http://franciscolima.com/en/eye-structure cc 
 
1. Fibrous tunic or Outer fibrous layer 
It is made up of Sclera and cornea. 
CORNEA 
Cornea is a transparent epithelial membrane forms the anterior surface of the eye in an 
area largely corresponding to the pigmented iris, which is visible behind the cornea.  
The cornea is formed by three cellular layers, which are separated from each other by two 
thin, acellular layers. Blood vessels are not normally found in the cornea, and the cells are 
not pigmented.  
The anterior surface of the cornea is lined by a stratified squamous epithelium. The 
posterior surface of the cornea is lined by an endothelium, the posterior endothelium. The 
lateral margins of the cornea are continuous with the conjunctiva (anterior corneal 
epithelium) and sclera (corneal stroma).