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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
Q

What kind of disease would show a blue sclera

A

Connective tissue diseases that cause scleral thinning

26
Q

Why might the sclera appear yellow

A

Presence of fatty deposits

Liver disease

27
Q

What are the two major foramina or canals of the sclera

A
  1. Anterior scleral foramen is the area occupied by the cornea
  2. The optic nerve passes through the poster scleral foramen
28
Q

What is the scleras weakest spot

A

Area where the optic nerve leaves the eye “Lamina Cribrosa”

29
Q

What is the “hole” where the optic nerve passes?

A

Not actually a hole, it is a mesh work of CT called the Lamina Cribrosa

30
Q

What is the weakest area of the outer connective tissue tunic

A

Lamina cribrosa

31
Q

Lamina cribrosa and high IOP

A

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
Q

Optic nerve cupping

A
  • 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
Q

If you can see the lamina cribrosa in a fundus photo, what does this indicate

A

It’s still healthy, it is just a deep cup

34
Q

Posterior scleral canals

A
  • 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
Q

Middle scleral canals

A

4 or more canals for the vortex

36
Q

Anterior scleral canal

A

7 canals for the anterior ciliary arteries

37
Q

How much blood supply to sclera

A

Minimum

38
Q

Why is the sclera considered avascular

A

A number of vessels pass through the sclera to other tissues but it contains no capillary beds itself

39
Q

Nourishment to the sclera

A

Furnished by small branches from the episcleral and choroidal vessels, and branches of the long posterior ciliary arteries

40
Q

Sensory innervation to the posterior sclera

A

Branches of the short ciliary nerves

41
Q

Sensory innervation of all f the sclera except the postier

A

Branches of hte long ciliary nerves

42
Q

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

A

Scleral ectasia

43
Q

Loose, vascularized, CT layer that lies just outer to the sclera

A

Episclera

44
Q

What is different between the sclera and the episclera

A

Episclera is loose, vascularized CT

45
Q

What vessels are visible through the conj

A

Larger episcleral vessels

46
Q

Form a capillary network in the episclaer just anterior to the rectus muscle insertions and surrounding peripheral cornea

A

Branches of the anterior ciliary arteries

47
Q

Where does the episclera become thinner

A

Towards the back of the eye

48
Q

What is the episclera joined by

A

Tenons capsule

49
Q

Episcleritis vs conjunctivitis

A

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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