Sclera - Layers (M2)

Question 1

how much of the fibrous layer of the globe does the sclera make up

Answer 1

85%

Question 2

what does the sclera surround

Answer 2

globe

Question 3

where does the sclera extend from anteriorly to posteriorly

Answer 3

extends from the limbus anteriorly to the optic nerve posteriorly.
merges with cornea anteriorly
merges with dural sheath of optic nerve posteriorly

Question 4

what is the sclera covered by

Answer 4

Tenon’s capsule and bulbar conjunctiva anteriorly

Question 5

what are the 3 layers that make up the sclera (outer to inner)

Answer 5

episclera
sclera
lamina fusca

Question 6

where is the sclera thickest and thinnest

Answer 6

thickest posteriorly near optic nerve.
decreases in thickness as approaches equator of the globe.
thinnest under the rectus muscles just before insertion.
increase in thickness at muscle insertion site.
increases in thickness towards limbus.

Question 7

thinnest layer of the sclera

Answer 7

episclera

Question 8

what does the episclera merge with

Answer 8

Tenon’s capsule and conjunctiva

Question 9

what is the episclera composed of

Answer 9

loose connective tissue (fibroblasts, collagenous fibers, ground substance)

Question 10

is the episclera vascularized or no?

Answer 10

highly vascularized

Question 11

composition of sclera

Answer 11

thick, irregular, dense connective tissue (fibroblasts, collagenous fibers, elastic fibers, ground substance)

Question 12

what type of collagen is predominant in the sclera

Answer 12

collagen type 1

Question 13

how does arrangement of collagen type 1 contribute to make up of sclera

Answer 13

contributes to strength and rigidity and white, opaque color

Question 14

how are collagen type 1 fibers arranged

Answer 14

grouped into bundles that are arranged into lamellae:
- outer lamellae course parallel to surface.
- inner lamellae course in all directions.
fibers are circularly arranged in the anterior, inner aspect of sclera, forming a ring.
- scleral spur

Question 15

where is elastin abundant in the sclera

Answer 15

deeper in the sclera, especially near the rectus muscle insertions and more posteriorly.
weaves between bundles of collagen fibers

Question 16

when would the sclera appear blue

Answer 16

if stroma is thin - occurs with age, in infants, and with collagen disease

Question 17

when would the sclera appear yellow

Answer 17

if fatty deposits builds up - with age.
if metabolic waste builds up - liver disease (jaundice)

Question 18

what is the lamina fusca adjacent to

Answer 18

choroid

Question 19

what does the lamina fusca provide

Answer 19

pigment - contains large # of melanocytes that migrate from choroid
(modified scleral stroma)