Download Human Beginning of Aravind Eye Care System

DEPARTMENT OF COUNSELLING
Basic Anatomy & Physiology of the eye
ARAVIND EYE CARE SYSTEM
Aravind Eye Hospital
& Postgraduate Institute of Ophthalmology
 The eye serves like camera, capturing the scenes
before it.
 The eyes are placed safe in a socket in the skull
and are protected by the eyelids
 Our eyes are more efficient than a film in a
camera, capturing the scenes and sending it to the
brain.
 The eye is spherical in shape.
 There are 6 extra ocular muscles present
outside of the eye which help in the movement
of eyes in various directions.
 The extra ocular muscles are supplied by nerves
from the brain.
 The eye ball is connected to the brain through a
nerve called optic nerve.
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Anatomy of the eye
Eye lids
Conjunctiva
Cornea
Anterior chamber
Iris
Pupil
Lens
Vitreous gel
Eyelids
 There are two eye lids – The upper eye lid and
lower eye lid
 The torsal plate helps in giving the structure to
the eye lid
 The eye lids protect the eyes from external
environmental pollution
Picture with
muscles
 Muscles connected to
the eye which are called
extra ocular muscles,
and are present outside
the eye.
 Superior rectus
 Medical rectus
 Lateral rectus
 Inferior rectus
 Superior oblique
 Inferior oblique
Conjunctiva
 This is a thin white membrane with blood
vessels covering the eye ball
Cornea
 The cornea is transparent
 It is like a window to the eye
 Cornea measures about 11.5 mm in horizontal
length
 There are five layers in cornea
Anterior Chamber
 The space between the cornea and Iris is called the
anterior chamber filled with aqueous humour, which
is secreated by a structure called ciliary body
 The depth of anterior chamber is 2.5 mm
 When the aqueous pressure in the eye increases the
condition is called Glaucoma
Iris & Pupil
 Behind the cornea there is a brown circular
diaphragm like structure called the Iris
 It consists of two types of muscles – Circular
muscles & Radial muscles
 The central opening of the Iris is called the pupil
 Normal size of pupil is 2-3 mm
 Depending on the intensity of light, the size of the
pupil increases or decreases in size
Lens
 Behind the Iris is situated, a transparent structure called the
lens
 The nutrition to the lens is supplied by the aqueous humour
 The shape of the lens is altered to see object at near and
distance
 Light rays passes through the lens and falls on the retina
 When the lens looses it transparency it becomes an opaque
structure, through which light cannot pass. This condition is
called as cataract
Vitreous gel
 There is a colorless, transparent gel like
substance behind the lens
 The vitreous gel is like the white of an egg
giving shape to the eye
The coats of the eye
 There are 3 coats of the eye
 Sclera
 Choroid
 Retina
Sclera
 The outer coat is the sclera, which is covered by
conjunctiva, a thin white membranous tissue
 The extra ocular muscles are inserted to the sclera
Choroid
 The choroid layer is middle coat situated
between sclera and retina
 The choroids tissue is dark brown in colour due
to vascularity
 It supplies nutrition to retina, vitreous and other
sensitive structures of the eye
 It also prevents the scattering of light
Retina
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The retina is made up of ten layers of neuronal tissues
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The retina is the inner most structure of the eye
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The rays coming from the objects fall on the retina
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Retina is basically transparent, cellophane, like tissue
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The optic disc is the head of the optic nerve entering the eye
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Arteries and veins course through the retina
 Macula is the most visually scientific
part of retina
 It is pink in colour with a central
depression called the optic disc cup
 In diseases like glaucoma where the
pressure in the eye is raised this cup is
enlarged
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Retinal Pigment epithelium
Layers of rods and cones
External limiting membrane
Outer nuclear layer
Outer Plexiform layer
Inner nuclear layer
Inner Plexiform layer
Ganglion cell layer
Nerve fiber layer
Internal – limiting membrane
The retinal receptors are divided into two main
populations – the rods and the cones
The rods functions best in dim light (night)
The cones functions best under daylight conditions
The cones are far fewer in number than the rods,
numbering 6 million, whereas the rods number 125
millions
Cones enable us to see small visual details with great
acuity
 Vision with rods is relatively poor
 Colour vision is totally dependent on the
integrity of the cones
 The cones from a concentrate area in the retina
known as the forea, which lies in the centre of
the macula lutea
 The junction of the periphery of the retina and
the ciliary body is called the Ora serratta
Functions of the eye
 The ability to see is an amazing process, made possible
by the parts of the eye working conjunction, with one
another and with the brain
 Light enters the eye through the transparent cornea, gets
refracted and then passes through the pupil to reach the
cones
 The pupil acts like the shutter of a camera
 In bright light, it becomes smaller, thus restricting the
 In less bright illumination and in darkness, the pupil
becomes larger, thus allowing adequate light to enter
the eye
 After light enters the pupil it passes through the
crystalline lens
 The refracted light then passes through the vitreous,
humour to reach the retina
 Here the light impulses are converted to electrical
impulses and then fed into the optic nerve, which
carries them to the visual centre in the brain through
a complex bundle of inter connected nerve channels
 The brain processes these impulses to create
the visual image we perceive
 Retina contains 3 corresponding types of cells
(cones) which respond to these three colours
 A defect in colour vision is called as colour
blindness. This can be partial, or total
 When we look at particular object, a lot of
other objects surrounding it are also perceived
 Hence our vision is not a small circle that we
focus on but a field in which we see multiple
object
 The visual field has two parts:
The central visual field which is the area
immediate to the object we are looking at and a
peripheral visual field which includes the rest
of the area surrounding the central field
 The eye balls are constantly in motion-up and
down, and either side
 This is facilitated by a group of six muscles,
where movements are synchronized by
interconnections in the brain to produce
conjugate movement
Ex: When we look to the right side the right
eye ball, moves outward whereas the left
eyeball moves inward
 An imbalance in this harmony result in a
disfigurment called squint or cross – eye.