The document provides an overview of the anatomy of the eye, detailing its various structures, including layers such as the sclera, choroid, and retina, as well as components like the cornea, iris, and lens. It describes the functions of these parts, such as focusing light, protecting the eye, and processing visual information through nerve impulses. Additionally, it outlines the eye's chambers, associated glands, and the roles of tear secretion in eye health.

1. Basic Anatomy of the
Basic Anatomy of the
Eye
Eye
National Eye Institute, National Institutes of Health

2. Basic Structure of the Eye
Basic Structure of the Eye
 The Eye is one part of the Visual System
The Eye is one part of the Visual System

The eye and focuses the image and detects
The eye and focuses the image and detects
the light
the light

The visual pathways transfer the nerve
The visual pathways transfer the nerve
impulses
impulses

The visual cortex in the brain processes the
The visual cortex in the brain processes the
signals, and we ‘see’ the image
signals, and we ‘see’ the image

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4. Layers of the wall of the eye
Layers of the wall of the eye
 The eye has three basic coats/layers:
The eye has three basic coats/layers:

Sclera
Sclera - the white, outer-most layer
- the white, outer-most layer
• Tough layer which gives the eye its shape, and protects it
Tough layer which gives the eye its shape, and protects it

Choroid
Choroid - middle layer, contains many blood
- middle layer, contains many blood
vessels
vessels
• Nourishes the outer portions of the retina
Nourishes the outer portions of the retina

Retina
Retina - inner-most layer, contains all the
- inner-most layer, contains all the
light-sensitive cells and nerves
light-sensitive cells and nerves

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6. Cornea
Cornea
 Transparent - light passes through it to
Transparent - light passes through it to
reach the retina
reach the retina
 Only 0.5mm thick
Only 0.5mm thick
 Main refracting component
Main refracting component
 Bulges out from the rest of the eye
Bulges out from the rest of the eye
 Not uniformly curved - it flattens towards
Not uniformly curved - it flattens towards
the limbus (where the cornea and sclera
the limbus (where the cornea and sclera
meet)
meet)

7. Conjunctiva
Conjunctiva
 Two parts:
Two parts:

Thin, transparent mucous membrane which
Thin, transparent mucous membrane which
covers the sclera over the front of the eye
covers the sclera over the front of the eye
from the cornea (
from the cornea (bulbar
bulbar conjunctiva)
conjunctiva)

Continuous with the skin at the lid margin
Continuous with the skin at the lid margin
(
(palpebral
palpebral conjunctiva)
conjunctiva)

The two meet in the
The two meet in the superior
superior/
/inferior
inferior fornices
fornices

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9. Anterior Chamber
Anterior Chamber
 Area which lies behind the cornea, but in
Area which lies behind the cornea, but in
front of the iris and lens
front of the iris and lens
 Contains a watery substance called the
Contains a watery substance called the
aqueous humour
aqueous humour

The aqueous humour is produced in the
The aqueous humour is produced in the
ciliary body and circulates around the anterio
ciliary body and circulates around the anterio
chamber, to drain through Schlemms’ Canal
chamber, to drain through Schlemms’ Canal

10. Iris
Iris
 This is a circular disc, with a hole in its
This is a circular disc, with a hole in its
center - the pupil
center - the pupil

The pupil size can be made bigger or smaller
The pupil size can be made bigger or smaller
by the iris muscles (4.5-8 mm)
by the iris muscles (4.5-8 mm)

The pupil controls the amount of light entering
The pupil controls the amount of light entering
the eye
the eye
 The iris gives the eye its colour
The iris gives the eye its colour
 determined by the amount of pigment
determined by the amount of pigment

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14. Ciliary Body
Ciliary Body
 Positioned between the iris and the choroid
Positioned between the iris and the choroid
 It is the point of attachment for the
It is the point of attachment for the zonular
zonular
fibers
fibers, which hold the lens in place
, which hold the lens in place
 It contains many muscles - when they relax, the
It contains many muscles - when they relax, the
zonular fibers relax. This allows the lens to
zonular fibers relax. This allows the lens to
change its shape, and it increase in dioptric
change its shape, and it increase in dioptric
power - this process is called accommodation
power - this process is called accommodation

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16. Posterior Chamber
Posterior Chamber
 Small area behind the iris, but in front of
Small area behind the iris, but in front of
the lens - contains aqueous humour
the lens - contains aqueous humour
 Do not confuse with vitreous chamber
Do not confuse with vitreous chamber
behind the lens
behind the lens

17. Lens
Lens
 Lens gives approx 1/3 of the eye’s dioptric
Lens gives approx 1/3 of the eye’s dioptric
power
power
 Consists of an inner core (nucleus), surrounded
Consists of an inner core (nucleus), surrounded
by a cortex
by a cortex
 Lens is covered by an elastic capsule, to which
Lens is covered by an elastic capsule, to which
the zonular fibres are attached
the zonular fibres are attached
 Back surface is more curved than the front
Back surface is more curved than the front
 Continues to grow throughout life, and becomes
Continues to grow throughout life, and becomes
less flexible. This reduces the accommodation
less flexible. This reduces the accommodation
and causes presbyopia. Eventually causes a
and causes presbyopia. Eventually causes a
cataract.
cataract.

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19. Vitreous Chamber
Vitreous Chamber
 Largest chamber
Largest chamber in the eye
in the eye
 Contains the vitreous humour (sometimes just called
Contains the vitreous humour (sometimes just called
‘vitreous’
‘vitreous’

Not watery like the aqueous, nor does it circulate
Not watery like the aqueous, nor does it circulate

It is a clear gel-like substance, which helps to support
It is a clear gel-like substance, which helps to support
the other parts of the eye
the other parts of the eye

Gets more watery and slightly yellow with increasing
Gets more watery and slightly yellow with increasing
age
age

Sometimes it shrinks in size as a person gets older –
Sometimes it shrinks in size as a person gets older –
posterior vitreous detachment
posterior vitreous detachment

It may pull on the retina and can sometimes cause a
It may pull on the retina and can sometimes cause a
retinal detachment
retinal detachment

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21. Choroid
Choroid
 Middle coat (layer) of the eye
Middle coat (layer) of the eye
 Largely composed of blood vessels
Largely composed of blood vessels
 Function is to nourish the outer portion of
Function is to nourish the outer portion of
the underlying retina
the underlying retina
 Very pigmented - this allows it to absorb
Very pigmented - this allows it to absorb
any stray light
any stray light

22. Retina
Retina
 Light sensitive layer of the eye
Light sensitive layer of the eye

The retina and visual pathways can be thought of as
The retina and visual pathways can be thought of as
an extension of the brain
an extension of the brain
 Consists of 10 layers
Consists of 10 layers, but is very thin:
, but is very thin:

0.1-0.23mm thick
0.1-0.23mm thick
 Contains two types of photoreceptors (the light
Contains two types of photoreceptors (the light
sensitive cells) called rods and cones
sensitive cells) called rods and cones
 Covers the innermost part of the eye - about 2/3
Covers the innermost part of the eye - about 2/3
of the surface
of the surface

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25. Optic Disc
Optic Disc
 The rods and cones are connected, in a complex
The rods and cones are connected, in a complex
way, with lots of other cell types in the retina
way, with lots of other cell types in the retina
 The rods and cones connect with the ganglion cells,
The rods and cones connect with the ganglion cells,
which join together to form the optic nerve
which join together to form the optic nerve
 The optic nerve leaves the back of the eye through a
The optic nerve leaves the back of the eye through a
hole (1.5x2mm) called the optic disc
hole (1.5x2mm) called the optic disc
 Optic disc can be seen by ophthalmoscopy
Optic disc can be seen by ophthalmoscopy
 There are no photoreceptors in the optic disc, so this
There are no photoreceptors in the optic disc, so this
produces a blind spot in our vision
produces a blind spot in our vision
 Demonstration exercise of blind spot
Demonstration exercise of blind spot

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28. Macula/Fovea
Macula/Fovea
 The macula is the part of the retina that has an
The macula is the part of the retina that has an
increased number of cone cells
increased number of cone cells

This area is about 5.5mm in diameter
This area is about 5.5mm in diameter
 The fovea (foveola) is the central part of the
The fovea (foveola) is the central part of the
macula (about 0.33mm in diameter)
macula (about 0.33mm in diameter)
 contains only cones
contains only cones
 It forms a depression in the macula, and is
It forms a depression in the macula, and is
responsible for the highest acuity
responsible for the highest acuity
 Retina is thinnest at the fovea
Retina is thinnest at the fovea

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30. Sclera
Sclera
 Tough, fibrous outer protective layer of the eye,
Tough, fibrous outer protective layer of the eye,
about 1mm thick
about 1mm thick
 Dense, white and continuous with the cornea
Dense, white and continuous with the cornea
 Largely responsible for giving the eye its shape
Largely responsible for giving the eye its shape
 The extra-ocular muscles are attached to the
The extra-ocular muscles are attached to the
sclera
sclera
 Sclera is thinnest where the optic nerve enters
Sclera is thinnest where the optic nerve enters
the eye - it has a sieve like appearance called
the eye - it has a sieve like appearance called
the lamina cribrosa
the lamina cribrosa

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32. Lids and Tears
Lids and Tears
 The lids are moveable folds of tissue that protect
The lids are moveable folds of tissue that protect
the eye
the eye
 They contain four different glands which
They contain four different glands which
contribute to the tear film
contribute to the tear film

Meibomian glands - the glands of
Meibomian glands - the glands of Zeiss
Zeiss and
and Moll
Moll -
-
produce oily layer on the surface of the tear film
produce oily layer on the surface of the tear film

Accessory lacrimal glands - the glands of Krause and
Accessory lacrimal glands - the glands of Krause and
Wolfring - supply most of the needed moisture to the
Wolfring - supply most of the needed moisture to the
cornea and conjunctiva
cornea and conjunctiva

34. Lacrimal Gland
Lacrimal Gland
 This is the tear secreting gland located above
This is the tear secreting gland located above
the eye
the eye
 Tears pass down over the cornea and
Tears pass down over the cornea and
conjunctiva, moistening the surface
conjunctiva, moistening the surface
 Tears drain into the puncta (small holes on the
Tears drain into the puncta (small holes on the
upper and lower lid margin)
upper and lower lid margin)
 They drain through small canals (the canaliculi)
They drain through small canals (the canaliculi)
into the nasolacrimal sac, and then into the nose
into the nasolacrimal sac, and then into the nose