Sclera And Epi Flashcards
What kind of connective tissue is the sclera? What is is continuous with?
- thick, dense connective tissue
- continuous with the corneal stroma at the limbus
Describe the collagen fibrils in the sclera and how they are arranged
- diameter carries from 25-230nm (not uniform)
- arranged in irregular bundles that branch and interlace
Name some differences in the cornea and the sclera collagen ****
- not uniform diameter in sclera (thin and narrow fibrils on the outside and thicker ones on the inside)
- not uniform lamellae orientation in sclera
- cornea is clear for healthy eyes and sclera is opaque in healthy eyes
Describe the lamella orientation in the sclera
- lamella in outer regions run parallel to the surface with interweaving between them
- lamella in inner regions run in all directions
What contributes to the strength and flexibility of the sclera?
- random arrangement and amount of interweaving between lamella
- interweaving gives flexibility despite absence of elastic fibers
Are there elastic fibers in the sclera?
- very very low incidence
- sometimes within bundles
Are fibroblasts in sclera?
-yea, but there are a lot less than cornea
What is the difference between the stromal ground substance of the cornea and the sclera?
Sclera has fewer GAGs than cornea
Does the sclera or the cornea have more moisture?
Cornea
What is the scleral spur?
- region or CIRCULARLY oriented collagen bundles that extend from the inner aspect of the sclera
- ring of collagen
- forms angle with Iris and cornea
What is the scleral spurs posterior edge in contact with? Anterior?
- posterior edge blends with oblique scleral fibers
- anterior edge collagen of the spur becomes continuous with trabecular mesh work
What are the factors that determine the opacity? Why is the sclera opaque?
- Number of GAGs-sclera has few
- Amount of water-sclera is dehydrated more than cornea (68%)
- Size and distribution of fibers-more variety means more scatter means more opaque
What could cause a blue sclera?
- babies: uveal layer shows through
- connective tissue disease- scleral thinning
What would cause a yellow sclera?
- fat deposits with age
- liver disease from build up of metabolic waste
What are the two MAJOR foramina/canals?
- Anterior scleral foramen-area occupied by the cornea
2. Posterior scleral foramen-optic nerve passes through
What is the weakest spot of the sclera?
- where the optic nerve leaves the eye
- Lamina cribrosa (mesh work of connective tissue)
What is the weakest area of the outer connective tissue tunic?
Lamina cribrosa
What is the area that is most affected by increased pressure?
Lamina cribrosa
What is cupping out/ectasia of the center area of the optic nerve causes by? What is it a sign of?
- elevated IOP
- glaucoma
- can also be attributed to loss of nerve fiber tissue of the optic nerve head
How many posterior scleral canals are there? What are they for?
- 2 for long ciliary nerves
- 2 for long ciliary arteries
- 8-12 for short ciliary arteries
- 8-12 for short ciliary nerves
How many middle scleral canals are there? What are they for?
-4 or more for vortex veins
How many anterior scleral canals are there? What are they for?
-7 for the anterior ciliary arteries
Why is the sclera considered avascular?
-it contains a small number of vessels that pass through to ge to other tissues, but it does not contain any capillary beds
How does the sclera get its nourishment>
-small branches from the episclera and choroidal vessels and branches of the long ciliary arteries
