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Ocular Block 6 > Sclera And Episclera > Flashcards

Sclera And Episclera Flashcards

1
Q

How much of the posterior of the connective tissue of the globe does the sclera make up

A

83%

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2
Q

What is the function of the sclera

A
  • shape
  • rigidity and resistance to external forces (and internal)
  • offers place to anchor EOMs
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3
Q

Thickness of sclera

A
  • 1mm near the posterior

- 3mm thick in the area where the rectus muscles attach

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4
Q

What kind of tissue is sclera

A

Thick, dense connective tissue layer that is continuous with the corneal stroma at the limbus

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5
Q

Diameter of the collagen fibrils in the sclera

A

25 to 230 nm

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6
Q

Why is the sclera opaque

A

Because collagen fibrils are not uniform

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7
Q

How are the fibrils of the sclera arranged

A

Irregular bundles that branch and interlace

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8
Q

Cornea or sclera? Uniform diameter and bundled in regular lamellar patterns

A

Cornea

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9
Q

Cornea or sclera? Collagen bundle widths and thicknesses vary, with the external bundles narrowe and thinner than the deeper bundles

A

Sclera

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10
Q

Cornea or sclera?Lamella is very irregular

A

Sclera

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11
Q

Sclera or cornea? Clear when healthy

A

Cornea

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12
Q

Why is the sclera strong

A

Because of irregularities in lamella

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13
Q

What contributes to the strength and flexibility of the eye

A

The random arrangement and the amount of interweaving of collagen fibrils in the sclera

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14
Q

The collagen of the EOM tendons and the sclera

A

Merges and interweaves with the fibrils of ther sclera

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15
Q

What is there a low incidence of in the sclera between and sometimes within bundles

A

Elastic fibers. Sclera not meant to stretch. Can cause thinning if stretched

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16
Q

What is present in the sclera but not as numerous as in the cornea

A

Fibroblasts

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17
Q

What is the biggest similarity between the cornea and the sclera?

A

The stromal ground substance is similar to the corneal ground substance but contains fewer GAGs

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18
Q

Region of circularly oriented collagen bundles that extends from the inner aspect of the sclera

A

Scleral spur

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19
Q

The scleral spur is actually a _________, although crosssections make it appear wedge shaped. Resembling a spur

A

Ring

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20
Q

What attaches to the scleral spur

A

Trabecular mesh work

21
Q

The opacity of the sclera depends on

A
  • The number of GAGs
  • The mount of water
  • Size and distribution of the collagen fibrils
22
Q

How many GAGs does the sclera contain compared to the cornea

A

Sclera contains 1/4 the number of GAGs that are present in the cornea, this makes the sclera relatively dehydrated compared with the cornea

23
Q

What is visible through the clear conj

A

Anteiror sclera

24
Q

Newborns and the sclera color

A

Bluish tint because it is almost transparent and the underlying vascular uvea shows through

25
What kind of disease would show a blue sclera
Connective tissue diseases that cause scleral thinning
26
Why might the sclera appear yellow
Presence of fatty deposits | Liver disease
27
What are the two major foramina or canals of the sclera
1. Anterior scleral foramen is the area occupied by the cornea 2. The optic nerve passes through the poster scleral foramen
28
What is the scleras weakest spot
Area where the optic nerve leaves the eye "Lamina Cribrosa"
29
What is the "hole" where the optic nerve passes?
Not actually a hole, it is a mesh work of CT called the Lamina Cribrosa
30
What is the weakest area of the outer connective tissue tunic
Lamina cribrosa
31
Lamina cribrosa and high IOP
Pushes on lamina cribrosa, which crimps the passages of when the nerves pass. Causes the nerves to slowly atrophy and die off Optic cupping
32
Optic nerve cupping
- lamina cribrosa most affected by high IOP in eye | - the cupping may be present in patients with high IOP and is one of the signs sometimes noted in glaucoma.
33
If you can see the lamina cribrosa in a fundus photo, what does this indicate
It's still healthy, it is just a deep cup
34
Posterior scleral canals
- 2 canals for the long ciliary nerve - 2 canals for the long ciliary arteries - 8-12 canals for short ciliary arteries - 8-12 canals for short ciliary nerves
35
Middle scleral canals
4 or more canals for the vortex
36
Anterior scleral canal
7 canals for the anterior ciliary arteries
37
How much blood supply to sclera
Minimum
38
Why is the sclera considered avascular
A number of vessels pass through the sclera to other tissues but it contains no capillary beds itself
39
Nourishment to the sclera
Furnished by small branches from the episcleral and choroidal vessels, and branches of the long posterior ciliary arteries
40
Sensory innervation to the posterior sclera
Branches of the short ciliary nerves
41
Sensory innervation of all f the sclera except the postier
Branches of hte long ciliary nerves
42
The progression of myopia causes by axial elongation in a highly myopic eye often causes this, particularly at the posterior pole where the collagen fibril diamter and the bundle size are reduced. The tissue bulges as it thins
Scleral ectasia
43
Loose, vascularized, CT layer that lies just outer to the sclera
Episclera
44
What is different between the sclera and the episclera
Episclera is loose, vascularized CT
45
What vessels are visible through the conj
Larger episcleral vessels
46
Form a capillary network in the episclaer just anterior to the rectus muscle insertions and surrounding peripheral cornea
Branches of the anterior ciliary arteries
47
Where does the episclera become thinner
Towards the back of the eye
48
What is the episclera joined by
Tenons capsule
49
Episcleritis vs conjunctivitis
Episcleritis: usually inflammation on one side of the eye, the vessels are deep Conjunctivitis: pink, flush, all over the eye.

Ocular Block 6 (7 decks)

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