Eye anatomy.pdf sclera retina layers of eye

Anatomy of eye

1. Anatomy of the eye
Peoples' Friendship University of Russia
named after Patrice Lumumba
Institute of Medicine
OPHTHALMOLOGY DEPARTMENT

2. Eyeball (Bulbus oculi)
Weight:newborn≈3g, adult (20-25years old)≈7,5g
Dimensions:sagittal–17,0mm sagittal–24,4mm
transverse-17,0mm transverse-23,8mm
vertical–16,5mm vertical–23,5mm
is a bilateral and spherical organ, which
houses the structures responsible for
vision. It lies in a bony cavity within the
facial skeleton – known as thebony orbit.

3. Anatomy of the Eyeball
1. Fibrous Tunic:
Cornea
Sclera
2. Vascular Tunic:
Choroid coat
Ciliary Body (Ciliary muscle, Ciliary process)
Iris
3. Nervous Tunic:
Retina

4. Fibrous layer
•Thescleracomprises the majority of the
fibrous layer (approximately 85%). It
provides attachment to theextraocular
muscles– these muscles are responsible for
the movement of the eye. It is visible as the
white part of the eye.
•Thecorneais transparent and positioned
centrally at the front of the eye. Light
entering the eye is refracted by the cornea.

5. Cornea
•The cornea is the eye’s optical
window that makes it possible for
humans to see.
•At 43 diopters, the cornea is the
most important refractive medium in
the eye.
•Diameter is 11,5 mm.
•The corneal tissue consists of five
layers. Nourishment: the cornea is a bradytrophic
tissue structure.
The cornea is nourished with nutritive
metabolites (amino acids and glucose)
from three sources:
•Diffusion from the capillaries at its edge.
•Diffusion from the aqueous
humor.
Diffusion from the tear film.

7. •Stratified nonkeratinized squamous epithelium that regenerates
quickly when injured. An intact epithelium protects against
infection; a defect in the epithelium makes it easy for pathogens to
enter the eye.
•Bowman’s layer is highly resistant but cannot regenerate. As a
result, injuries to Bowman’s layer usually produce corneal scarring.
•The stroma is a highly bradytrophic tissue. As avascular tissue, it
only regenerates slowly. However, its avascularity makes it an
immunologically privileged site for grafting. Routine corneal
transplants may be performed without prior tissue typing.
•Descemet’s membrane is a relatively strong membrane. It will
continue to define the shape of the anterior chamber even where
the corneal stroma has completely melted (see Descemetocele).
Because it is a genuine base- ment membrane, lost tissue is
regenerated by functional endothelial cells.
•The corneal endothelium is responsible for the transparency of the
cornea. A high density of epithelial cells is necessary to achieve
this. The corneal endothelium does not regenerate; defects in the
endothelium are closed by cell enlargement and cell migration.

8. Vascular layer
•Choroid– layer of connective tissue and blood
vessels. It provides nourishment to the outer layers of
the retina.
•Ciliary body– comprised of two parts – the ciliary
muscle and ciliary processes. The ciliary muscle
consists of a collection of smooth muscles fibres.
These are attached to the lens of the eye by the ciliary
processes. The ciliary body controls the shape of the
lens, and contributes to the formation of aqueous
humor
•Iris– circular structure, with an aperture in the centre
(the pupil). The diameter of the pupil is altered by
smooth muscle fibres within the iris, which are
innervated by the autonomic nervous system. It is
situated between the lens and the cornea.

9. Iris
The iris consists of two layers:
❖ The anterior mesodermal stromal layer.
❖ The posterior ectodermal pigmented epithelial
layer.
The posterior layer is opaque and protects the eye
against excessive incident light. The anterior surface
of the lens and the pigmented layer are so close
together near the pupil that they can easily form
adhesions in inflammation.
The collarette of the iris covering the minor arterial
circle of the iris divides the stroma into pupillary and
ciliary portions.
The pupillary portion contains the sphincter muscle,
which is supplied by parasympathetic nerve fibers,
and the dilator pupillae muscle, supplied by
sympathetic nerve fibers. These muscles regulate the
contraction and dilation of the pupil so that the iris
may be regarded as the aperture of the optical system
of the eye.

10. Intrinsic Eye Muscles and
their response to light
The pupillary portion contains the sphincter muscle, which is supplied by parasympathetic
nerve fibers, and the dilator pupillae muscle, supplied by sympathetic nerve fibers.
These muscles regulate the contraction and dilation of the pupil so that the iris may be
regarded as the aperture of the optical system of the eye.

11. The color of the iris varies in the individual according to the melanin content of
the melanocytes (pigment cells) in the stroma and epithelial layer.
Eyes with a high melanin content are dark brown, whereas eyes with less
melanin are grayish-blue.
Caucasians at birth always have a grayish-blue iris as the pigmented layer only
develops gradually during the first year of life.
Even in albinos, the eyes have a grayish- blue iris because of the melanin
deficiency. Under slit lamp retroillumination they appear reddish due to the
fundus reflex.

12. Ciliary Body
•The ciliary body extends from the root of the
iris to the ora serrata, where it joins the
choroid.
•It consists of anterior pars plicata and the
posterior pars plana, which lies 3.5mm
posterior to the limbus. Numerous ciliary
processes extend into the posterior chamber of
the eye. The suspensory ligament, the zonule,
extends from the pars plana and the intervals
between the ciliary processes to the lens
capsule.
•Function: The ciliary muscle is responsible
for accommodation. The double- layered
epithelium covering the ciliary body produces
the aqueous humor.

13. Choroid
•The choroid forms part of the
vascular layer of theeyeball,
along with theciliary
bodyandiris.
•It is a thin, pigmented
vascularconnective tissue layer
of the eyeball that extends from
the ora serrata to theoptic nerve.
•It is formed of five main layers
(from internal to external):
–bruch's membrane,
–the choroiocapillaris,
–the two vascular layers (Haller's and
Sattler's),
–the suprachoroidea.

14. Choroid
•The choroid receives its rich
vascular supply from theshort
and long posterior ciliary
arteriesand is drained by
thevorticose veins.
•The vessel walls of the choroid
receiveparasympathetic
innervationfrom
thepterygopalatine
ganglionandsympathetic
innervationfrom thesuperior
cervical ganglion.
•The choroid regulates
temperature and supplies
nourishment to the outer layers
of the retina.

15. Inner layer
The inner layer of the eye is formed by theretina; its light detecting component.
The retina is composed of two layers:
•Pigmented (outer) layer– formed by a single layer of cells. It is attached to the
choroid and supports the choroid in absorbing light (preventing scattering of light
within the eyeball). It continues around the whole inner surface of the eye.
•Neural (inner) layer– consists of photoreceptors, the light detecting cells of the
retina. It is located posteriorly and laterally in the eye.
Anteriorly, the pigmented layer
continues but the neural layer
does not – this is part is known
as thenon-visual retina.
Posteriorly and laterally, both
layers of the retina are present.
This is theopticpart of the
retina.

16. Opthalmoscopic view of the retina showing
the location of the Macula to the Optic Disc
The optic part of the retina can be
viewed duringophthalmoscopy.
The centre of the retina is marked by
an area known as themacula.
It is yellowish in colour, and highly
pigmented. The macula contains a
depression called thefovea
centralis, which has a high
concentration of light detecting cells.
It is the area responsible for high
acuity vision.
The area that the optic nerve enters
the retina is known as the optic disc
– it contains no light detecting cells.

17. Histology of the retina of the eye

18. Structures of the
Eyeball
•Vitreous body
•Lens
•Aqueous Humor

19. Vitreous body
Thevitreous bodyis a transparent gel
which fills the posterior segment of the
eyeball (the area posterior to the lens).
It is marked by a narrow canal which runs
from the optic disc to the lens –
thehyaloid canal. This is a fetal remnant.
The vitreous body has three main
functions:
✓Contributes to the magnifying power
of the eye
✓Supports the lens
✓Holds the layers of the retina in place

20. Lens
Function of the lens:
The lens is one of the essential refractive media of
the eye and focuses incident rays of light on the
retina.
It adds a variable element to the eye’s total
refractive power (10 – 20 diopters, depending on
individual accommodation) to the fixed refractive
power of the cornea (approximately 43 diopters).
Shape:
The fully developed lens is a biconvex, transparent
structure. The curvature of the posterior surface,
which has a radius of 6 mm, is greater than that of
the anterior surface, which has a radius of 10 mm.
Metabolism and aging of the lens:
The lens is nourished by diffusion from the aqueous
humor. In this respect it resembles a tissue culture,
with the aqueous humor as its substrate and the
eyeball as the container that provides a constant
temperature.

21. Lens
•The lens lies in the posterior chamber of the eye between the posterior
surface of the iris and the vitreous body in a saucer- shaped depression of the
vitreous body known as the hyaloid fossa.
•Together with the iris it forms an optical diaphragm that separates the
anterior and posterior chambers of the eye.
•Radially arranged zonule fibers that insert into the lens around its equator
connect the lens to the ciliary body. These fibers hold the lens in position and
transfer the tensile force of the ciliary muscle.

22. Accommodation of the Lens
for near vision
•Ciliary muscles contract
•Ciliary body pulls forward and inward
•Tension on suspensory ligaments of lens is
decreased
•Lens becomes thicker (rounder) due to its
elasticity
•Pupils constricts

23. Accommodation of the Lens
for far vision
•Ciliary muscles relaxes
•Ciliary body returns to its resting state, backward
and outward
•Tension on suspensory ligaments of lens is
increased
•Lens becomes thinner (flatter) due to its elasticity
•Pupils dilate

24. Anterior and
Posterior Chambers
There are two fluid filled areas in the eye – known as
theanteriorandposterior chambers.
The anterior chamber is located between the cornea and the iris,
and the posterior chamber between the iris and ciliary
processes.
The chambers are filled withaqueous humor– a clear plasma-
like fluid that nourishes and protects the eye. The aqueous
humor is produced constantly, and drains via the trabecular
meshwork, an area of tissue at the base of the cornea, near the
anterior chamber.
If the drainage of aqueous humor is obstructed, a condition
known asglaucomacan result.

25. Detail view of the anterior anatomy
of the eye

26. Production of Aqueous Humor and
Intraocular pressure
1.Ciliary Process:
Produces Aqueous Humor
2. Posterior Chamber:
Aqueous Humor passes from
this chamber through the
pupil in Anterior Chamber
3.Canal of Schlemm
Reabsorbs Aqueous Humor

27. External Anatomy of the Eye

28. Accessory structures
of the eye
•Orbit (orbita)
•Extraocular Muscles (musculus bulbi)
•Eyelids (palpebrae)
•Conjunctiva
•Lacrimal organs

29. The Eyelids
•The eyelids are folds of muscular soft
tissue that lie anterior to the eyeball and
protect it from injury.
•Their shape is such that the eyeball is
completely covered when they are closed.
•Strong mechanical, optical, and acoustic
stimuli (such as a foreign body, blinding
light, or sudden loud noise)
“automatically” elicit an eye closing
reflex.
•The cornea is also protected by an
additional upward movement of the
eyeball (Bell’s phenomenon).
•Regular blinking (20 – 30 times a minute)
helps to uniformly distribute glandular
secretions and tears over the conjunctiva
and cornea, keeping them from drying
out.

30. Structure of the eyelids
❖Superficial layer:
– Thin, well vascularized layer of skin.
– Sweat glands.
– Modified sweat gland and sebaceous glands (ciliary glands or glands of Moll) and sebaceous
glands (glands of Zeis) in the vicinity of the eyelashes.
– Striated muscle fibers of the orbicularis oculi muscle that actively closes the eye (supplied by
the facial nerve).
❖ Deep layer:
– The tarsal plate gives the eyelid firmness and shape.
– Smooth musculature of the levator palpebrae that inserts into the tarsal plate (tarsal muscle).
The tarsal muscle is supplied by the sympathetic nervous system and regulates the width of the
palpebral fissure. High sympathetic tone contracts the tarsal muscle and widens the palpebral
fissure; low sympathetic tone relaxes the tarsal muscle and narrows the palpebral fissure.
– The palpebral conjunctiva is firmly attached to the tarsal plate. It forms an articular layer for
the eyeball. Every time the eye blinks, it acts like a windshield wiper and uniformly distributes
glandular secretions and tears over the conjunctiva and cornea.
– Sebaceous glands (tarsal or meibomian glands), tubular structures in the cartilage of the
eyelid, which lubricate the margin of the eyelid. Their function is to prevent the escape of tear
fluid past the margins of the eyelids. The fibers of Riolan’s muscle at the inferior aspect of
these sebaceous glands squeeze out the ducts of the tarsal glands every time the eye blinks.

32. Orbital Cavity
Importance of the orbital cavity for the eye:
The orbital cavity is the protective bony socket for
the globe together with the optic nerve, ocular
muscles, nerves, blood vessels, and lacrimal gland.
These structures are surrounded by orbital fatty
tissue. The orbital cavity is shaped like a funnel
that opens anteriorly and inferiorly. The six ocular
muscles originate at the apex of the funnel around
the optic nerve and insert into the globe. The globe
moves within the orbital cavity as in a joint socket.
Bony socket: This consists of seven bones:
❖ Frontal.
❖ Ethmoid.
❖ Lacrimal.
❖ Sphenoid.
❖ Maxillary.
❖ Palatine.
❖ Zygomatic.
The bony rim of the orbital cavity forms a strong
ring.

33. Orbital Cavity
The close proximity of the orbital cavity to adjacent structures is clinically
significant. The maxillary sinus inferior to the orbital cavity is separated from it by
a plate of bone 0.5 mm thick. The ethmoidal air cells located medial and posterior
to the orbital cavity are separated from it by a plate of bone only 0.3 mm thick or
by periosteum alone. The following other structures are also located immediately
adjacent to the orbital cavity.
❖ Sphenoidal sinus.
❖ Middle cranial fossa.
❖ Region of the optic chiasm.
❖ Pituitary gland.
❖ Cavernous sinus.
Because of this anatomic situation, the orbital cavity is frequently affected by
disorders of adjacent structures. For example, inflammations of the paranasal
sinuses can result in orbital cellulitis.

34. Orbital Cavity

35. Extraocular muscles
The movements of the eyeballs are produced
by the following extraocular muscles:
❖ The four rectus muscles: the superior,
inferior, medial, and lateral rectus
muscles.
❖ The two oblique muscles: the superior and
inferior oblique muscles.
All of these muscles originate at the tendinous
ring except for the inferior oblique muscle,
which has its origin near the nasolacrimal
canal.
The rectus muscles envelope the globe
posteriorly, and their respective tendons insert
into the superior, inferior, nasal, and temporal
sclera.
The oblique muscles insert into the temporal
globe posterior to the equator. The insertion of
the muscles determines the direction of their
pull.

36. Conjunctiva
•The conjunctiva is a thin vascular mucous membrane that
normally of shiny appearance. It forms the conjunctival sac
together with the surface of the cornea. The bulbar
conjunctiva is loosely attached to the sclera and is more
closely attached to the limbus of the cornea.
•There the conjunctival epithelium fuses with the corneal
epithelium.
•The palpebral conjunctiva lines the inner surface of the
eyelid and is firmly attached to the tarsus.
•The loose palpebral conjunctiva forms a fold in the
conjunctival fornix, where it joins the bulbar conjunctiva.

37. Function of the conjunctival sac
•Motility of the eyeball. The loose connection
between the bulbar conjunctiva and the sclera and
the “spare” conjunctival tissue in the fornices allow
the eyeball to move freely in every direction of
gaze.
•Articulating layer. The surface of the conjunctiva is
smooth and moist to allow the mucous membranes
to glide easily and painlessly across each other. The
tear film acts as a lubricant.
•Protective function.The conjunctiva must be able
to protect against pathogens. Follicle-like
aggregations of lymphocytes and plasma cells (the
lymph nodes of the eye) are located beneath the
palpebral conjunctiva and in the fornices.
Antibacterial substances, immunoglobulins,
interferon, and prostaglandins help protect the eye.
The conjunctival
sac has three main
tasks:

39. Lacrimal Apparatus of the Eye
The lacrimal system consists of two sections:
❖ Structures that secrete tear fluid.
❖ Structures that facilitate tear drainage.

40. Structures that secrete tear fluid
•The lacrimal gland is about the size of a walnut; it lies beneath the superior
temporal margin of the orbital bone in the lacrimal fossa of the frontal bone
and is neither visible nor palpable.
•A palpable lacrimal gland is usually a sign of a pathologic change such as
dacryoadenitis.
•The tendon of the levator palpebrae muscle divides the lacrimal gland into a
larger orbital part (two-thirds) and a smaller palpebral part (one-third).
•Several tiny accessory lacrimal glands (glands of Krause and Wolfring)
located in the superior fornix secrete additional serous tear fluid.
•The lacrimal gland receives its sensory supply from the lacrimal nerve.
Its parasympathetic secretomotor nerve supply comes from the nervus
intermedius. The sympathetic fibers arise from the superior cervical sympathetic
ganglion and follow the course of the blood vessels to the gland.

41. Tear film
The tear that moistens the conjunctiva and cornea is composed of
three layers:

42. Tear drainage
•The shingle-like arrangement of the fibers of the orbicularis oculi muscle
(supplied by the facial nerve) causes the eye to close progressively from lateral
to medial instead of the eyelids simultaneously closing along their entire
length. This windshield wiper motion moves the tear fluid medially across the
eye toward the medial canthus.
•The superior and inferior puncta lacrimales collect the tears, which then drain
through the superior and inferior lacrimal canaliculi into the lacrimal sac.
From there they pass through the nasolacrimal duct into the inferior concha.

43. The anatomy of the visual pathway may be divided into six separate parts:
1. Optic nerve: This includes all of the optic nerve fiber bundles of the
eye.
2. Optic chiasm: This is where the characteristic crossover of the nerve
fibers of both optic nerves occurs. The central and peripheral fibers from
the temporal halves of the retinas do not cross the midline but continue
into the optic tract of the ipsilateral side. The fibers of the nasal halves
cross the midline and there enter the contralateral optic tract. Along the
way, the inferior nasal fibers travel in a small arc through the proximal end
of the contralateral optic nerve (the anterior arc of Wilbrand). The superior
nasal fibers travel in a small arc through the ipsilateral optic tract (the
posterior arc of Wilbrand).
3. Optic tract: This includes all of the ipsilateral optic nerve fibers and
those that cross the midline.

44. 4. Lateral geniculate body: The optic tract ends here. The
third neuron connects to the fourth here, which is why
atrophy of the optic nerve does not occur in lesions beyond
the lateral geniculate body.
5. Optic radiations (geniculocalcarine tracts): The fibers of
the inferior retinal quadrants pass through the temporal lobes;
those of the superior quadrants pass through the parietal lobes
to the occipital lobe and from there to the visual cortex.
6. Primary visual area (striate cortex or Brodmann’s area 17
of the visual cortex): The nerve fibers diverge within the
primary visual area; the macula lutea accounts for most of
these fibers. The macula is represented on the most posterior
portion of the occipital lobe. The central and intermediate
peripheral regions of the visual field are represented
anteriorly. The temporal crescent of the visual field, only
present unilaterally, is represented farthest anteriorly.

45. Visual Pathway
1.Cones
2.Bipolar neurons
3.Ganglion cell’s axon forms the optic nerve
4.Optic nerve to the Optic Chiasm
5.Optic tract
6.Lateral geniculate nuclei of the thalamus
7.Optic Radiations
8.Primary visual areas of the occipital lobes

46. The Visual Pathway

47. Light Refractory
Pathway:
1.Bulbar Conjunctiva
2.Cornea
3.Aqueous Humor
4.Lens
5.Vitreous Humor
6.Ganglion Cell Layer
7.Inner Synaptic Layer
8.Bipolar Layer
9.Outer Synaptic Layer
10. Photoreceptor Layer