Anatomy of the eye and Layers of eyeball in which you can learn about the anatomy of the different structure of the 3 layers of eyeball

2. Layers of eyeball
By
Anam Sehreen
Doctor of optometry

3. Eyeball
 The ball of eye is known as eyeball. It is the organ of
vision lying in the orbital cavity which protects it from
the external injuries.
 Each eyeball is a cystic structure kept distended by the
pressure inside it.
 However, generally referred to as a globe, the eyeball
is not a sphere but an ablate spheroid in shape.

4. Eyeball
 The central point on the maximal convexities
of the anterior and posterior curvatures of the
eyeball is called the anterior and posterior
pole, respectively.
 The equator of the eyeball lies at the mid
plane between the two poles.

5. Anterior and posterior pole of
eyeball

6. Anatomical structures/layers/wall of
eyeball
There are three layers/coats of eyeball
1. The outer layer (fibrous coat) : Sclera and cornea
2. The middle layer (vascular coat) : Iris, ciliary body and choroid
3. The inner layer (nervous coat) : Retina

7. Three
layers/coats
of eyeball

8. 1. The Outer Fibrous Layer
 It is also known as tunica externa/tunica fibrosa.
 It is a dense strong wall which protects the intraocular contents.
 It is a corneoscleral layer which gives protection and shape to the different structures
of the eyeball.
 It is divided into following parts: sclera and cornea

9. 1. The Outer Fibrous Layer
Scler
a
Corne
a
Scleral corneal
sinus

10. Cornea
 Cornea is the anterior 1/6th of the fibrous coat, transparent, ellipsoid, and front part of the
eyeball.
 There is no blood vessels but lots of nerve endings in the cornea.
 It is described as the “window of the eye”.
 Cornea is set into sclera like a watch glass, thus it is a part of sclerotic coat.
 It is the main refracting surface of the eye.
 The dioptric power is + 43D to + 45 D.
 Light rays pass through the cornea to reach the retina.

12. Sclera
 Sclera is the white part of the eye that forms a firm, fibrous outermost layer of the eye.
 It is the posterior 5/6th opaque, fibrous, collagenous, tough and dense part of the outer
fibrous layer.
 It maintains the spherical shape of the eye and gives attachment to the extraocular muscles
(EOM).
 It’s thickness about 1 mm.
 It becomes thin (seive-like membrane) at the place where the optic nerve pierces it known
as Lamina cribrosa.

13. Sclera
 Functions of sclera:
 It provides protection to the delicate structure within the eye
 It resists intraocular pressure
 It maintains shape of the eyeball
 The smooth external surface allows easy eye movement.

14. Sclera

15. Limbus
 The junction of cornea and sclera is known
as the limbus.
 There is a minute arcade of blood vessels
about 1 mm broad present at the limbus.
 A transitional zone about 2 mm wide that
contains trabecular meshwork through
which aqueous humour is drained.

16. Conjunctiva
 Conjunctiva is a thin, transparent mucous
membrane that covers the eyeball.
 It is firmly attached at the limbus.
 There are three types of conjunctiva.
1) Bulbar conjunctiva
2) Palpebral conjunctiva
3) Forniceal conjunctiva
Superior
palpebral
conjunctiv
a
Bulbar
conjunctiv
a on
sclera
Inferior
palpebral
conjunctiv
a

17. Canal of Schlemm
 Canal of Schlemm is a venous passages
that drains the fluid which accumulates
behind the cornea.
 Location: It is located where the sclera and
cornea meet.

18. 2. The Middle Vascular Layer
 It is a vascular coat (uveal tissue), tunica media
or tunica vasculosa.
 This layer contains blood vessels, thus it
supplies nutrition to the various structures of
the eyeball.
 It consists of three parts which from anterior to
posterior are: iris, ciliary body and choroid.
 All these three parts together form uveal tract

19. Iris
 Iris is a free, circular diaphragm and a pigmented (colored)
membrane.
 It arises from the margin of ciliary body and forms a dark
centered opening (aperture) called pupil.
 It divides the anterior segment of the eye into anterior and
posterior chambers which contain aqueous humour secreted by
the ciliary body.

20. Iris
 Iris consists of endothelium, stroma, pigment cells.
 This colored portion of eye is formed by two groups of plain (smooth) muscle fibers, one
circular (sphincter pupillae) and the other radiating (dilator pupillae) which regulate the
amount of light entering the eye by constricting or dilating the pupil respectively.

21. Pupil
 Rounded opening of the iris through which light
passes know as pupil.
 An internal margin of the iris surrounding the pupil
known as the pupillary margin.
 Pupil size varies from 1 to 8 mm managed by the
two pupillary muscles.
 Function: It controls the amount of light entering the
eye.

22. Ciliary body
 Ciliary body is triangular in shape with base forwards and is the continuation of choroid
consisting of smooth muscle fibers (intrinsic muscle) known as ciliary muscles which
support and modify the lens shape.
 Ciliary body is the light sensitive membrane.
 The iris is attached to the middle of the base.
 It contains suspensory ligament for attaching the lens in position and ciliary muscles help
in accommodation by adjusting the thickness of lens.

23. Ciliary body

24. Ciliary body
 It consists of non-striated muscle fibers (ciliary muscles), stroma and secretory epithelial cells.
 It consists of two main parts, namely pars plicata and pars plana.
 It produces aqueous humour through its ciliary processes.

25. Choroid
 Choroid is a thin pigmented membrane, dark brown, highly
vascular layer situated between the sclera (externally) and
retina (internally).
 It extends from the ora serrata up to the aperture of the
optic nerve in the sclera.
 As it is a vascular layer so it provides nutrition to the outer
layers of retina.
 Function: It supplies blood vessels to the eye and contains
dark pigment granules that prevents the reflection of light
in the eye.

26. 3. The Inner Nervous Tissue Layer
 It is also known as tunica interna/tunica nervosa.
 Its parts are: Retina, optic disc, optic nerve

27. Retina
 Retina lines about 3/4 of the eyeball. It is the innermost
thin delicate layer of the eye and lines its surface
posteriorly with optic nerve and contains
photoreceptors (cells responsible for converting light
into nerve impulses known as rods and cones).
 It converts the light energy into the electrical energy
(action potential) which is transmitted via the visual
pathway to the occipital cortex.

28. Retina
 Retina is composed of ten layers of nerve cells and nerve fibers lying on a pigmented
epithelial layer. It consists of:
 Inner layer: Sensory retina, is in contact with the hyaloid membrane of the vitreous
 Outer layer: Retinal pigment epithelium (pigment cells), attached to choroid
 Macula lutea is a yellow area of the retina situated in posterior part with a central
depression called fovea centralis.
 It is the most sensitive part of retina and concerned with visual functions.

29. Retina

30. Optic disc
 The small area of retina where the optic nerve leaves the eye is the optic disc/blind spot.
 It is a circular, pink colored disc of 1.5 mm diameter.
 It has only nerve fiber layer so it does not excite any visual response.
 Area where optic nerve attaches to the retina has no light sensitive cells (rods and cones)
or photoreceptors.

31. Optic disc

32. Optic nerve
 The optic nerve extends from the lamina cribrosa up to the optic chiasma.
 The total length of the optic nerve is 5 cm.
 It has four parts namely:
 Intraocular :1 mm
 Intra-orbital : 25 mm
 Intraosseous : 4-10 mm
 Intracranial : 10 mm (Duke–Elder)