The document summarizes the anatomy and structures of the human eye. It describes the accessory structures like eyelids, lacrimal apparatus, and extraocular muscles. It then details the three tunics that make up the eyeball: the fibrous tunic (cornea and sclera), vascular tunic (choroid, ciliary body, and iris), and nervous tunic (retina). Each tunic and their roles in vision are explained. The interior structures of the cornea, retina, and their functions in processing light and forming images are outlined.

1. Hasan A. Mokbel
Medicals International
Contact lens Department
The Anatomy of the Eye

2. The Eye
Accessory
structures
Eyeball
Structures
Interior of
the eye ball
structures

3. 1. Accessory Structures
 Eye lids
 Eye Lash
 Eye brows
 Lacrimal apparatus
 Conjunctiva
 Tear film
 Extra ocular muscles

4. Eye Lids
 It’s a movable thin skin folds covering the eyes
 Plays a role in the protection of the eye from
injury by rapid closure.
 The eye lids include the tarsal glands that
secretes oily material for lubrication and prevents
evaporation of tears and stabilize the tear film.

5. Eye Lash & Eye brows
 The eye lashes and eye brows provide extra
protection for the eye by preventing the entrance
of microbial agents and dust and other matter that
can cause harm to the eye.

6. Lacrimal Apparatus

7. Lacrimal Apparatus
 The Lacrimal apparatus is made up of many
structures that is involved in nutrition , protection
against pathogens and hydration roles.
 The Lacrimal gland is located superior to the eye
lids and is an exocrine gland ( secretes in a duct
).

8. Lacrimal Apparatus
 The Lacrimal ducts dump the tears on the surface
of the conjunctiva coming from the Lacrimal
gland directly and they range from 6 to 12 duct.
 The Lacrimal puncta are 2 opening that collects
the tears from conjunctiva and drains them to
Lacrimal canal.
 The Lacrimal canal starts at the Lacrimal punctum
and ends at the Lacrimal sac , it delivers the tears
to the Lacrimal sac.

9. Lacrimal Apparatus
 The nasolacrimal duct descends from the
Lacrimal sac to open at the meatus in the nose.

10. The Conjunctiva
 The Conjunctiva is a transparent mucosal layer
that extends from the corneal junction to the inner
portion of the eye.
 The Conjunctiva is divided into 2 parts : Bulbar &
Palpebral.
 The Bulbar conjunctiva is thin , slightly vascular
and surrounds the eye ball.
 The Palpebral is dense , highly vascular and
located in the inner layer of the lid .

11. The Tear film
 The tear film have 3 layers :
 Lipid layer : is the outermost layer
and is produced by Meibomian gland forms
a hydrophobic barrier to trap water and prevent
its evaporation.
 Aqueous (watery) layer : is the layer between
lipid and mucous layer and contains water and
proteins which has bactericidal activity also the
aqueous layer regulates the osmotic pressure .

12. The Tear film
 The mucus layer : is produced by goblet cells
found in the conjunctiva and provide a hydrophilic
layer to ensure the even distribution of tears
along the tear film.

13. Extra Ocular Muscles
 The extra ocular muscles spread along the eye
ball and maintains the flexible movement of the
eye .
 There are 7 muscles :
i. The palpebral superior muscle : thin muscle
that lifts the upper lid.
ii. The four recti ( superior , inferior , medialis and
lateralis) : the superior rectus enables the
upward movement , the inferior downwards ,
the medialis inward and finally the lateralis
outwards movement.
iii. The oblique muscles ( superior obliquus and
inferior obliquus muscle )

14. 2. Eye ball structures
Eye ball
Fibrous tunic Vascular tunic
Nervous tunic
( Retina)

15. Fibrous tunic
 Is the outer covering of the eye it includes :
a. The cornea
b. The sclera

16. The Cornea
 Dome shaped , transparent and non vascularized
layer.
 Forms the outer cover of the eye .
 Contains highly organized cells and collagen
fibers.
 Should remain transparent to ensure correct
refraction of light.
 Serves as a shield against bacteria , dust and
harmful materials.
 Gets its nourishment from the aqueous humor
surrounding it.

17. The cornea
 The cornea is composed of 5 layers
1) The epithelial layer
2) The bowman’s membrane
3) Stroma
4) Descemet’s membrane
5) Endothelium

18. The cornea
 The epithelial layer : is the outermost layer of the
cornea it includes 5 to 7 layers of epithelial cells :
1. Squamous cells layer : is covered by microvilli
that absorbs the tears and keep the epithelial
cells hydrated.
2. The wing cell layer : composed of wing cells
that is attached to each other via desmosomes
which provide them with communicating
abilities.
3. The basal cell layer : basal cells play a role in
renewing the layer by multiplication and
providing new wing cells that migrate to change
to new squamous cells which replace the old
squamous layer cells .

19. The cornea

20. The cornea
 The epithelial cells layer provide barrier to dust
and infectious agents and prevents the
electrolytes from tears to reach the stroma.
 The epithelial cells provide also a soft surface
that is permeable to oxygen and nutrients via
lacrimation.

21. The cornea
 Bowman’s Membrane : contains collagen fibers
and once injured regeneration is impossible.
 Stroma layer :
• Thickest layer of the cornea .
• Contains : 78 % water , 16 % collagen and keratocytes.
• It has a unique arrangement of collagen fibers in which they
maintain the transparency of the cornea.
• The space between collagen fibers and keratocytes is filled
with ground substance made up of keratin sulfate and
chondroitin sulfate.

22. The cornea
 The Descemet’s membrane has 2 different layers
in which the side facing the stroma have collagen
fibers and the side facing the endothelium have
endothelial cells .
 Descemet’s membrane have the ability to
regenerate after injury.
 Descemet’s membrane provide shield against
injury and infection

23. The cornea :
 The Endothelial layer is the innermost layer of the
cornea.
 The Endothelial layer pumps from the stroma the
any excess fluid and prevents its swelling
therefore it has a role in maintenance of a clear
and transparent cornea.
 The Endothelium lacks the ability to regenerate
after injury.

24. The cornea
 The main function of the cornea is to refract light
and direct it towards the lens .
 The lens accommodates and refocus the light on
the retina .
 The retina transfers the image to nervous impulse
that is transmitted to the brain via the optic nerve
 The brain analyses the image .
 The cornea also eliminates the UV light rays from
the sun which is harmful for the human eye.

25. The sclera
 The sclera is the outer covering of the eye except
for the area of the cornea.
 It provide protection and shape to the eye.
 Its superior to the choroid and posteriorly is
pierced to the optic nerve
 The sclera is composed of :
 Elastic fibers
 Collagen fibers
 Fibroblasts
 Blood vessels

26. Vascular tunic ( uvea )
 Is the middle layer of the eye and is composed of
3 constituents :
o The choroid
o The ciliary body
o Iris

27. The Choroid
 Is located inferior to the sclera and superior to the
retina.
 Dark brown tissue.
 Highly vascularized.
 It provides the retina with nutrients and oxygen.
 The choroid prevents the
scattered light from reaching
the retina.

28. The Ciliary Body
 The ciliary body is divided into 2 parts :
 The Ciliary processes : which have secretary
function .
 The ciliary muscles : which have mechanical
function.

29. The Ciliary Body
 The ciliary processes is responsible to secrete the
aqueous humor to the anterior cavity to supply
the lens and cornea with nutrients since they are
not vascularized.
 Aqueous humor contains glucose and amino
acids and respiratory gases.

30. The Ciliary Body
 Ciliary muscles are responsible for the
accommodation of the lens by contraction and
relaxation which changes the shape of the lens to
flat or sphere depending on the distance of the
object.

31. Iris
 The iris is located between the lens and the
cornea .
 The iris divides the eye ball into anterior and
posterior chambers.
 The iris have 2 muscles :
 Sphincter muscles : contracts in high light exposure and the pupil
reduces its diameter allowing less light to pass.
 Dilator muscles : contracts at low light exposure and the pupil will
dilate its diameter allowing more light to pass.

32. Nervous tunic ( Retina )
 The Retina is located below the choroid .
 Is where the image is formed and transferred to brain via
optic nerve.
 Composed of 10 layers :
1. Retinal Pigment epithelium.
2. The lamina of cones & rods.
3. External limiting lamina
4. Outer nuclear layer
5. Outer plexiform layer
6. Inner nuclear layer
7. Inner plexiform layer
8. Ganglion layer
9. Lamina of nerve fibers
10. The internal limiting lamina

33. Retina
 Retinal pigment layer :
 Contains melanin containing epithelial cells between choroid and
neural portion.
 Its involved in the renewal of rod and cones photoreceptor cells
by phagocyting the old aging cells.
 Also the retinal pigment layer absorbs light and prevents the
reflection and scattering of light.

34. The neural portion
 It includes all the 9 layers above the retinal
pigment layer.
 Its responsible for the early analysis of visual
information before sending to the brain.
 The neurons are classified through which light
passes through:
1. The ganglion cell layer
2. The bipolar cell layer
3. Photoreceptor layer

35. The neural portion

36. The neural portion
 The ganglion layer : is the final common pathway
that the nerve impulse crosses since their
dendrites reach the bipolar cells and the axons
extends to the CNS.
 The bipolar cell layer : each cell with one or more
dendrites extending to the cones or rods and
horizontal cells and interplexiform cells , they
have short axons and they are 2 types :
 Cone bipolar cells communicate with cone cells.
 Rod bipolar cells communicate with rod cells .

37. The neural portion
 Photoreceptor layer : ( the layer of cones and rods ) it
transduces the light to the receptor due to the
presence of :
120x10^6 rod neuron
6x10^6 cone neuron
both cones and rods
have outer segment
and inner segment
together they form a
cone or a rod process .
The inner segment decides if the photoreceptor is a
cone or a
Rod.

38. The neural portion
 The rods are responsible for the black and white
vision and they are more than cones and they are
concentrated at the peripheral retina and
decreases in number as you reach the fovea.
 The cones are responsible for the colored vision
and they are less in number than rods and they
are concentrated(25 000) at the fovea in the
macula which is a depression where the retina is
extremely thin making the choroid beneath
visible.

39. The neural portion
 These photo pigment are made up of glycoprotein
called opsin and a chromatophore forming the
cis-retinal a derivative of vitamin A.
 Retinal undergoes structural change when
exposed to light and this change initiates a
nervous impulse across the nerves.

40. The neural portion
 Retinal photo pigment is found in 2 isomer forms :
 Cis-Retinal (inactive form )
 Trans-Retinal ( active form )
 At day time Cis-Retinal gets exposed to light it gets
activated and releases opsin and undergoes a
structural change to trans-retinal form which causes
the inhibition of glutamate neurotransmitter release
and causes the closure of sodium channels which
causes a hyper polarization and initiation of a nervous
impulse along the nerves.

41. The neural portion
 The trans-retinal form causes the activation of an
enzyme transducin enzyme.
 Transducin enzyme will activate another enzyme
called Phosphodieseterase (PDE) causing the closure
of Na channels.
 Na ions decrease inside the cell and by that the
charge intracellular will decrease until it unleashes an
action potential .
 At night time when the light is too low to activate the
rhodopsin and release a nerve impulse , glutamate
neurotransmitter is highly secreted which transports
the impulse.

42. The Interior eye ball
 The Eye ball is divided by the lens into 2 parts :
 The anterior cavity .
 The posterior cavity ( the vitreous cavity).

43. Eye ball
 The Anterior cavity includes 2 sections :
 Anterior chamber ( between cornea and iris )
 Posterior chamber ( between iris and the lens )
 Anterior cavity is filled with aqueous humor. The
aqueous humor is rich in glucose nutrients and
respiratory gases its used to enrichment of the
unvascularized organs.
 The vitreous chamber is filled with vitreous
humour which is colorless gel like constancy due
to the presence of collagen fibers.
 Vitreous humour also keeps the retina in place by
pushing it against the choroid.

44. The lens
 The eye lens is located between vitreous humour and
the iris
 The eye lens is 9 to 10 mm in diameter.
 Attached to the ciliary body via thin filaments called
zonula fibers.
 The lens is made up of 3 parts :
o Nucleus
o Capsule
o Cortex
 The lens is unvascularized and transparent
 The lens fibers are rich with :
 Crystalline ( gives the elasticity and retractile properties ).
 Actin ( maintain the shape of the lens.

45. The End