EYEBALL
EYEBALL is the sensory organ of vision lying in the orbital cavity surrounded by orbital fat
but separated from it by a fascial sheath known as tenon’s capsule which allows free
movement of the eyeball. The eyeball consists of three layers or coats.
Outer fibrous (corneoscleral) layer
It gives shape and protection to the structures of the eyeball. It is divided into the following
parts:
Cornea:
1: it is a transparent avascular structure that comprises anterior one-sixth of the outer layer.
2:It is composed of five layers, epithelium, bowmen's membrane, stroma, descemet’s
membrane and endothelium.
3: it provides the proper anterior refractive surface for the eye and contributes to two-third of
the refractive power of the eye.
Sclera:
1:it is the dense, fibrous, collagenous structure that comprises posterior five-sixth of the
outer layer.
2:It maintains the shape of the eyeball and protects it from injuries.
3:It gives attachment to the extraocular muscles.
Limbus:
1:It is a transitional zone about 2 mm wide between the transparent cornea and opaque
sclera.
2:It contains trabecular meshwork through which the aqueous humor is drained and is a site
of surgical incision for cataract and glaucoma.
3:It is the location of the limbal stem cells which provides epithelial cells to the cornea.
Middle vascular (Uveal) Coat
It is divided into three parts:
Choroid:
1: It is the posterior ⅔ vascular layer and consist of:
● Outermost layer of the larger diameter blood vessels.
● layer of medium diameter blood vessels.
● Highly fenestrated capillary bed known as the choroid.
● Bruch’s membrane - innermost layer of the choroid.
2:It supplies nutrients and oxygen to the outer layers of the retina.
Ciliary body:
1:it is the middle part of the uvea.
2:It is composed of the ciliary muscle and ciliary process.
3:The ciliary body produces aqueous humor through its ciliary processes and takes part in
accommodation through the muscular portion.
Iris:
1:Iris is the most anterior part of the uvea. It is the thin pigmented structure which acts as a
diaphragm with the central aperture called pupil.
2:The iris consists of two layers: the front pigmented fibrovascular layer known as a stroma
and, beneath the stroma, pigmented epithelium cells.
3:The stroma is connected to the sphincter muscles.
● Sphincter pupillae: which contracts the pupil
● Dilator muscles which pull the iris radially and enlarge the pupil
EYEBALL is the sensory organ of vision lying in the orbital cavity surrounded by orbital fat
but separated from it by a fascial sheath known as tenon’s capsule which allows free
movement of the eyeball. The eyeball consists of three layers or coats.
Outer fibrous (corneoscleral) layer
It gives shape and protection to the structures of the eyeball. It is divided into the following
parts:
Cornea:
1: it is a transparent avascular structure that comprises anterior one-sixth of the outer layer.
2:It is composed of five layers, epithelium, bowmen's membrane, stroma, descemet’s
membrane and endothelium.
3: it provides the proper anterior refractive surface for the eye and contributes to two-third of
the refractive power of the eye.
Sclera:
1:it is the dense, fibrous, collagenous structure that comprises posterior five-sixth of the
outer layer.
2:It maintains the shape of the eyeball and protects it from injuries.
3:It gives attachment to the extraocular muscles.
Limbus:
1:It is a transitional zone about 2 mm wide between the transparent cornea and opaque
sclera.
2:It contains trabecular meshwork through which the aqueous humor is drained and is a site
of surgical incision for cataract and glaucoma.
3:It is the location of the limbal stem cells which provides epithelial cells to the cornea.
Middle vascular (Uveal) Coat
It is divided into three parts:
Choroid:
1: It is the posterior ⅔ vascular layer and consist of:
● Outermost layer of the larger diameter blood vessels.
● layer of medium diameter blood vessels.
● Highly fenestrated capillary bed known as the choroid.
● Bruch’s membrane - innermost layer of the choroid.
2:It supplies nutrients and oxygen to the outer layers of the retina.
Ciliary body:
1:it is the middle part of the uvea.
2:It is composed of the ciliary muscle and ciliary process.
3:The ciliary body produces aqueous humor through its ciliary processes and takes part in
accommodation through the muscular portion.
Iris:
1:Iris is the most anterior part of the uvea. It is the thin pigmented structure which acts as a
diaphragm with the central aperture called pupil.
2:The iris consists of two layers: the front pigmented fibrovascular layer known as a stroma
and, beneath the stroma, pigmented epithelium cells.
3:The stroma is connected to the sphincter muscles.
● Sphincter pupillae: which contracts the pupil
● Dilator muscles which pull the iris radially and enlarge the pupil
