Sclera

Question 1

Name the layers of the sclera

Answer 1

1) episclera
2) scleral stroma
3) lamina fusca

Question 2

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 corner-scleral junction?

Answer 2

a) 1mm at posterior pole
b) 0.3mm behind insertion of extra ocular muscles
c) 0.6mm
d) 0.8mm

Question 3

Name the four structures that perforate the sclera

Answer 3

1) optic nerve + fibres
2) anterior ciliary arteries
3) ciliary nerves
4) vortex veins

Question 4

Where does the optic nerve attach to the sclera?
What is the sclera fused with here?

Answer 4

3mm medial and 1mm superior to the anatomical posterior pole

Fused with dural and arachnoid sheaths of optic nerve

Question 5

What is the name of the area of sclera perforated by optic nerve fibres?

Answer 5

Lamina cribrosa

Question 6

Where do the anterior ciliary arteries pierce the sclera?
How many arteries pierce the sclera?

Answer 6

at insertion of each RECTUS muscle
Two arteries per muscle, except LR which has only 1
(ie 7 arteries)

Question 7

Can you induce ocular ischaemic syndrome by recessing oblique muscles? Justify your answer

Answer 7

NO. Oblique muscles do not contribute to anterior arterial circle

Question 8

Where do the long and short ciliary nerves piece the sclera? Describe briefly their course in the orbit

Answer 8

Next to the optic nerve head
Travel anteriorly within perichoroidal space

Question 9

Where do the vortex veins piece the sclera?
How many are there?

Answer 9

4mm posterior to equator
2 veins in superior hemisphere and 2 in inferior hemisphere

Question 10

Describe the structure of the episclera
is it connected to anything?

Answer 10

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

Question 11

Blood supply of episclera anteriorly

Answer 11

from anterior ciliary arteries
form 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

Question 12

a) Describe structure of scleral stroma
b) What is the diameter of collagen fibre?

Answer 12

a) Randomly arranged fibrous collagen (T1 and 3) + elastic fibres
b) 8-280nanometers

Question 13

Are any cells found in the scleral stroma?

Answer 13

flat, elongated fibroblasts
Occasional melanocyte

Question 14

How does sclera respond to deforming forces?
Why?

Answer 14

Biphasic response:
1) elastic response –> brief lengthening
2) viscid response –> slow stretching

Bc it is viscoelastic

Question 15

What colour is the lamina fusca?

Answer 15

Faint BROWN
Bc there are melanocytes

Question 16

Describe the structure of the lamina fusca

Answer 16

thin, irregular layer with many grooves (caused by passage of ciliary vessels and nerves)

Question 17

Describe the relation between the lamina fusca and the choroid

Answer 17

Separated from choroid by potential space “perichoroidal space”
fine, weak collagen fibres attach the two structures

Question 18

What is the blood supply to the posterior sclera?

Answer 18

Small branches from long and short posterior ciliary arteries

Question 19

What is the nerve supply of the sclera?

Answer 19

Ciliary nerves (which pierce the sclera around the optic nerve)
Short ciliary nerves supply posterior sclera, long ciliary nerves supply anterior sclera

Question 20

What kind of pain does scleritis produce?
What typically makes scleritis pain worse?

Answer 20

dull pain
movement of EOM (because these insert into sclera)

Question 21

What is the function of the sclera?

Answer 21

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

Question 22

Colour of sclera through life

Answer 22

Childhood - blue tinge as still thin, can see underlying choridal pigment cells
Adulthood = white
Old age = yellow tinge due to fat deposits

Question 23

Why is sclera blue in Ehlers-Danlos, osteogenesis imperfecta etc?

Answer 23

Defect in collagen synthesis => can see underlying choroidal pigment

Question 24

Why is sclera yellow in jaundice?

Answer 24

Br in vasculature gives yellow appearance

Question 25

Where is globe most likely to rupture after blunt injury?

Answer 25

at thinner points - muscle insertion

Question 26

Where is the most common site of extra-ocular extension of intra-ocular tumours?

Answer 26

Optic nerve
Although can extend anywhere where sclera is pierces (ie vortex veins, anterior ciliary arteries, long + short ciliary nerves

Question 27

What is ciliary flush and what is it associate with?

Answer 27

Vasodilation episcleral plexus (formed from ciliary arteries)
Associated with inflammation cornea, iris, ciliary body