Sclera Flashcards
pg 124-128
Name the layers of the sclera
1) episclera
2) scleral stroma
3) lamina fusca
a) Where is the sclera thickest? + how thick
b) Where is the sclera thinnest? + how thick
c) How thick is the sclera at the equator?
d) How thick is the sclera at the corneo-scleral junction?
a) 1mm at posterior pole
b) 0.3mm behind insertion of extra ocular muscles
c) 0.6mm
d) 0.8mm
Name the four structures that perforate the sclera
1) optic nerve + fibres
2) anterior ciliary arteries
3) ciliary nerves
4) vortex veins
Where does the optic nerve attach to the sclera in relation to the posterior pole?
What is the sclera fused with here?
3mm medial and 1mm superior to the anatomical posterior pole
Fused with dural and arachnoid sheaths of optic nerve
What is the name of the area of sclera perforated by optic nerve fibres?
Lamina cribrosa
Where do the anterior ciliary arteries pierce the sclera?
How many arteries pierce the sclera?
at insertion of each RECTUS muscle
Two arteries per muscle, except LR which has only 1
(ie 7 arteries)
Can you induce ocular ischaemic syndrome by recessing oblique muscles? Justify your answer
NO. Oblique muscles do not contribute to anterior arterial circle
Where do the long and short ciliary nerves piece the sclera? Describe briefly their course in the orbit
Next to the optic nerve head
Travel anteriorly within perichoroidal space
Where do the vortex veins piece the sclera?
How many are there?
4mm posterior to equator
2 veins in superior hemisphere and 2 in inferior hemisphere
Describe the structure of the episclera
is it connected to anything?
External layer of sclera lying just internal to Tenon’s capsule
Connects to tenon’s capsule at points by fine connective tissue
Comprised of loose connective tissue
Merges with underlying scleral stroma
Becomes progressively thinner towards back of eye
Blood supply of episclera anteriorly
from anterior ciliary arteries
form episcleral plexus that extends between the extrinsic muscle insertions + corneoscleral junction (it it’s anterior lol)
Lie deep to conj
These are the vessels that become inflamed in episcleritis :p
a) Describe structure of scleral stroma - WHAT TYPE OF COLLAGEN?
b) What is the diameter of collagen fibre?
c) How far are they from each other?
a) Randomly arranged fibrous collagen (T1 and 3) + elastic fibres
b) 28-280microns
c) periodicities of 80 and 21microns
Are any cells found in the scleral stroma?
**flat, elongated fibroblasts **
Occasional melanocyte
How does sclera respond to deforming forces?
Why?
Biphasic response:
1) elastic response –> brief lengthening
2) viscid response –> slow stretching
Bc it is viscoelastic
What colour is the lamina fusca?
Faint BROWN
Bc there are melanocytes
Describe the structure of the lamina fusca
thin, irregular layer with many grooves (caused by passage of ciliary vessels and nerves)
Describe the relation between the lamina fusca and the choroid
Separated from choroid by potential space “perichoroidal space”
fine, weak collagen fibres attach the two structures
What is the blood supply to the posterior sclera?
Small branches from long and short posterior ciliary arteries
What is the nerve supply of the sclera? + what is nerve supply of anterior vs posterior sclera?
Ciliary nerves (which pierce the sclera around the optic nerve)
Short ciliary nerves supply posterior sclera, long ciliary nerves supply anterior sclera
What kind of pain does scleritis produce?
What typically makes scleritis pain worse?
dull pain
movement of EOM (because these insert into sclera)
What is the function of the sclera?
1) To protect the intraocular contents from trauma/mechanical displacement
2) preserves shape of eyeball and therefore position of optic system
3) provides rigid insertion point for muscles
Colour of sclera through life
Childhood - blue tinge as still thin, can see underlying choridal pigment cells
Adulthood = white
Old age = yellow tinge due to fat deposits
Why is sclera blue in Ehlers-Danlos, osteogenesis imperfecta etc?
Defect in collagen synthesis => can see underlying choroidal pigment
Why is sclera yellow in jaundice?
Br in vasculature gives yellow appearance
Where is globe most likely to rupture after blunt injury?
at thinner points - muscle insertion
Where is the most common site of extra-ocular extension of intra-ocular tumours?
Optic nerve
Although can extend anywhere where sclera is pierces (ie vortex veins, anterior ciliary arteries, long + short ciliary nerves
What is ciliary flush and what is it associate with?
Vasodilation episcleral plexus (formed from ciliary arteries)
Associated with inflammation cornea, iris, ciliary body
