2. The sclera (from the Greek skleros, meaning hard,
also known as the white or white of the eye, is the
opaque (usually white, though certain animals, such as
horses and lizards, can have black sclera), fibrous,
protective, outer layer of the eye containing collagen
and elastic fiber.
3. SCLERA
The sclera is a dense fibrous collagenous
structure
that comprises the posterior 5/6 of the eye.
Anteriorly it forms the white of the eye.
In adult the sclera is white ,in children,when the
sclera is thin ,the pigment cells of the choroid
shows through,giving the sclera a bluish tinge.in
the elderly the sclera may a yellowish tinge from
the deposition of fat.It might be noted that the
yellow appearnce of the eyeball in jaundice is
due not to pigment in the sclera but to bilirubin
in the vascular conjuctiva.
4. it is covered with fascial sheath of the
eye ball (Tenon’s capsule) and the
conjunctiva.
Posteriorly the sclera is connected by
delicate connective tissue to the fascial
sheath of the eyeball.
5. In the adult the sclera is about 1 mm
thick posteriorly, thinning at the
equator to 0.6 mm. It is thinnest 0.3
mm immediately posterior to the
insertion of recti muscles.
6.
7. The sclera has two large openings
the anterior and
posterior scleral foramen
and numerous small openings through
which nerves and blood vessels pass.
8. The sclera is perforated 3 mm medial &1mm
above the posterior pole of the eye ball by
the optic nerve.the site of this perforation is
sometimes referred to as the posterior scleral
foramen.here the sclera is fused with the
dural and arachnoid sheaths where the optic
nerve fibers pierce the sclera it is weakened
and has a sieve like appearance and is
known as the lamina cribrosa.its relatively
weak area ,it can be made to bulge outward
by a rise in intraocular pressure,producing a
cupped disc.
9. The anterior scleral foramen is bridged by cornea.
The sclera is thickest in the region
surrounding the optic nerve. It is
thinnest immediately posterior to the
insertion of recti muscles. Inflammation of the sclera
will cause a dull,aching pain,since the extraocular
muscle are inserted in to the sclera at thinnest
reagen of the sclera ,the pain is made worse by
ocular movement.
10. The sclera is also pierced by three
groups of small apertures
anterior
middle &
posterior.
11. The anterior apertures are located at
the insertion of the recti muscles and
are for branches of the anterior cilliary
arteries.
12. The middle apertures are situated
about 4-mm posterior to the equator of
the eye and number about four or five.
They are for the exit of the vortex veins.
13. and numerous and are located around
optic nerve. They transmit the long
and short cilliary nerves and vessels.
The posterior apertures are small
14. Sclera is directly connected with cornea
anteriorly, the line of union is known as
corneoscleral junction.
17. The episclera
the outer most layer
it is moderately dense,
vascularised, connective tissue.
It has rich blood supply that may
become congested in inflammation.
18. consists of
collagen fibers.
The fibers are parallel to corneoscleral
limbus.
in the region of insertion of extraocular
muscles they become more meridional in
response to stress induced by traction of
ocular muscles.
The scleral stroma
19. Lamina fusca
the innermost layer of the sclera
located next to choroid
which provides melanocytes that gives
it a brown colour
20. Endothelium
Sclera contains a basal endothelium,
above which there is the lamina fusca,
containing a high count of pigment
cells.
22. Long and short cilliary nerves.
Nerve supply
23. Functions
The tough fibrous structure of the
sclera protects the intraocular contents
from trauma and mechanical
displacement.
24. The firmness and strength of the sclera,
together with the intraocular pressure,
preserves the shape of the eyeball and
maintain the exact position of the
different parts of the optic system.
25. The strength and firmness of the sclera
provide a rigid insertion for the
extraocular muscles.
