The eyeball is a spherical structure having 2.5 diameters. Structurally, the eyeball has three layers:- sclerotic layer (outer layer);  choroid (middle layer) and retina (inner layer). Outermost layer contains sclera and cornea Middle layer contains choroid, ciliary body and iris. Innermost layer consists of retina

1. EYE IMAGE: HOW TO EXPLAIN EYE
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EYE IMAGE
STRUCTURE OF EYE:
IT’S WORKING AND PROBLEMS
The eyeball is a spherical structure having 2.5 diameters. Structurally, the eyeball has three layers:-
sclerotic layer (outer layer); choroid (middle layer) and retina (inner layer).
PARTS OF THE HUMAN EYE
 Outermost layer contains sclera and cornea
 Middle layer contains choroid, ciliary body and iris.
 Innermost layer consists of retina
AN OVERVIEW OF STRUCTURE, LOCATION, FUNCTIONS
OF VARIOUS PARTS OF THE EYE
PARTS OF THE
EYE
STRUCTURE LOCATION
FUNTION
Sclera
Opaque fibro-elastic
capsule; transparent in
front at cornea
Outermost covering
part of eye
i)Maintains shape of
eyeball
ii)Protects inner eye
Lacrimal gland Saclike structure
Upper eyelid towards
the outer corner of eye.
i)Secretions wash away
dust particles
ii)Lubricates eye
iii)lysozyme present in
tear kills the germs
Cornea
Transparent buging
part
Front part of eye
i)Allows the light to
pass into the eye.

2. ii)Helps in focusing.
Conjunctiva Thin transparent layer
Present over the
cornea.
Protects cornea.
Choroid
Pigmented layer
containing numerous
blood vessels.
Present in middle layer
beneath the sclera.
i)Prevents reflection
within eye.
ii)Provides eye.
Ciliary body
Contains ciliary muscle
and blood vessels.
Present at the junction
of sclera and the
cornea.
Helps to maintain shape
of eye.
Ciliary muscle
Contains a complex set
of smooth muscles in a
circular form.
Present over
suspensory ligaments
The contraction of
ciliary muscles results
in spherical shape of the
lense and the relaxation
in the flattened shape.
Suspensory ligamentsThread-like ligaments
Attached to the ciliary
body to the lens.
They hold lend in
position.
Iris
Pigmented circle of
muscular diaphragm.
Attached to the ciliary
body.
It controls the size of
pupil for entry of
amount of light.
Pupil
Small aperture or
opening of eye.
Present in the centre of
pupil.
It helps in entering
light into the eye.
Retina
Stretched light
sensitive screen-like
structure containing
two types of
photoreceptor- rods
and cones.
Present at the
innermost layer of eye.
An inverted image of
the object is formed at
the retina.
Fovea or yellow spot
Contains cone cells
only.
Present in depressed
part of of retina.
It helps to form the
sharpest image .
Blind spot
Non-light sensitive
area as does contain
rods and cones.
Present at the area of
retina from where the
optic nerve leaves the
eye.
No image is formed.
Optic nerve
Contains fibres of the
sensory neurons.
It leaves the eyeball
from the back side of
the eye.
It transports impulses
for vision to the brain.
Lense
It is a transparent,
elastic and biconvex
structure which is non-
nucleated, transparent
and elongated cells.
Hold by suspensory
ligaments.
It undergoes a change
in thickness and brings
the adjustment for
focusing of light on
retina.
COMPARTMENTS:
The lens, ciliary body and suspensory ligaments divide the eyeball into two compartments:-

3. Anterior and Posterior which are filled by the solutions aqueous humour and the vitreous
humour respectively.
COMPARATIVE STUDY OF TWO TYPES OF SOLUTIONS
CHARACTER AQUEOUS HUMOUR VITREOUS HUMOUR
i)Type Clear, watery salt solution.
Clear , transparent jelly-like
substance.
ii)Occurrence
Anterior compartment of the
eye.
Posterior compartment of the
eye.
iii)Position
Present between the cornea
and the lens.
Present between the lens and
retina.
iv)Function
i)It supplies nutrition to the
lens and cornea.
ii)It maintains the shape of the
cornea.
iii)It supports the lens by its
pressure.
i)It helps in maintaining the
shape of eye-ball.
ii)It supports both lens and
retina.
IMAGE FORMATION ON THE RETINA
The formation of an image on the retina requires four steps:-
 Refraction of light rays
 Accommodation of the lens
 Constriction of the pupil
 Convergence of the rays
i)REFRACTION OF THE LIGHT RAYS:- Focuses an image by refracting, or bending the light rays using
cornea and the lens. At the yellow spot of retina an inverted image is formed. Most of the refraction of light
occurs in cornea due to its curved surface.
ii)ACCOMODATION:- In a normal eye, an object at a distance 6metre away would be in perfect focus on the
retina. The process of focusing by the eye at different distances is called accommodation. This process is
brought by adjusting the curvature of the elastic lens making it thinner or thicker.

4. In distant vision, (more than 6 metres) the ciliary muscles are relaxed and the lens becomes flatter or thinner
due to stretching of the suspensory ligaments.
In near vision, (less than 6metres) the ciliary muscles contract pulling the choroid forward, towards the lens
and tension is released on the suspensory ligaments. The lens becomes shortened, more convex and
thickened due to its elastic nature.
In normal condition the ciliary muscles and are relaxed and the lens remain stretched by the sensory
ligament. Then, it is less convex and best suited for the distant vision.
STEREOSCOPIC VISION:- Humans have two eye, both are frontally placed on the face. When both eyes
focus on the same object, each eye produces a slightly different image as each eye views from different
angles. Stereoscopic vision occurs when for the same object , each eye forms it own separate image of the
object on the retina and the vision fields of both the eyes overlap in the center.
Here are some events for the stereoscopic vision:-
 The brain correlates the two images and resolves it into one image only.
 The stereoscopic vision depends on where the eye are located.
 If the eyes are more frontally located , the stereoscopic vision is greater.
 The perception of distance and depth is due to simultaneous focusing of an object in both the eyes and
overlapping gives a three-dimensional image.
ADVANTAGES OF STEREOSCOPIC VISION:-
 Stereoscopic vision gives larger visual field than monocular vision( vision by single eye)
 It gives increased accuracy of size and perception of depth and distance of object.

5. WORKING OF EYE
The working of eye is similar to that of a camera except that the lens of human eye does not move forward
or backward but adjusts the distance for focus by undergoing changes in its shape.
PHOTORECEPTION
EYE PHOTOGRAPHIC CAMERA
Lense muscle Camera focusing aperture
Eyelid Lense cap
Eye ball Camera box
Pupil Lense aperture
Lense Lense
Iris Diaphragm
Retina Photographic film or plate
 When the light rays from any object fall on cornea, they enter the eye through pupil.
 Iris controls the amount of light passing through by controlling the size of pupil.
 The rays of light converge as they pass through the cornea, aqueous humour, lens and vitreous
humour and finally focus at retina forming an inverted image of the object.
 The light rays are bent at the cornea and the lens makes the final adjustment to bring a sharp focus on
retina.
The inverted image formed at the retina is picked by the optic nerve which takes it to the brain where it is
reversed and finally an upright image of the object is perceived by the individual.
COMMON DEFECTS OF VISION
NAME OF
THE
DEFECTS
SYMPTO
MS
REASON
CORRECTI
VE
MEASURE
RELATED DIAGRAM

6. Myopia or
near-
sightedness
i)Person
cannot see
distant
objects
clearly
ii)The
person can
see nearby
objects
clearly.
i)Eyeball is
lengthened
ii)Lens is too
much curved
or too convex .
Use of
concave
lense.
Hypermetrop
ia or long
sightedness
Person
cannot see
nearby
objects
clearly.
i)Eyeball is
shortened.
ii)lens is too
flat or less
curved.
Use of
biconvex
lense
Astigmatism
Formation
of blurred
image .
Uneven
curvature of
cornea
Use of
cylindrical
lense.
Presbyopia
(old age long
sightedness)
Affects
older
people
(after 40)
cannot see
distant or
nearby
object
clearly.
i)Loss of
flexibility of
lens.
ii)Failure of
accommodatio
n.
Use of bifocal
lense.
No Image
Cataract or
sofia motia
Hazy
vision.
Lens becomes
opaque.
Surgical
removal of
lens and
No Image

7. implantation
of artificial
lens or use of
spectacles
with convex
lens.
Glucoma or
kala motia
Person
cannot see
at all.
i)secretion of
aqueous
humour is
increased.
ii)intraocular
pressure is
increased.
Cured by
drugs if
detected on
time.
No Image