Lecture 7: Sclera

What type of tissue is the sclera made of?

Thick and dense connective tissue

What are the functions of the sclera?

• Maintain shape and globe size

• Shock absorption

• Attachment site for EOMs

• Anchor for intraocular contents

What is the diameter and radius of curvature of the sclera?

Diameter: ~24 mm

Radius: ~11.5 mm

The sclera has a ________ radius of curvature than the cornea.

Larger (means it is also flatter)

List the thickness of the sclera from thinnest area to the thickness area.

• Thinnest: ~0.3 mm posterior to EOM insertions

• ~0.8 mm at limbus

• Thickest: ~1.0 mm at posterior pole

What is the sclera composed of?

• Water (68%)

• Collagen

• Fibroblasts

• Proteoglycans (e.g. GAGs)

• Elastin fibers

What type of collagen is commonly found in sclera?

Type I

How is sclera collagen organized? What does this result in?

• Irregular organization

• It interweaves more than cornea → strength and rigidity.

What helps the sclera maintain hydration and collagen spacing?

Proteoglycans

What is the scleromuscular junction?

A site where sclera collagen merges with collagen of EOM tendons.

What does red, blue, and yellow scleral color mean?

Red = dilated / hyperemic blood vessels

Blue = thin sclera

Yellow = liver disease

What are the three layers of the sclera from most external to internal?

1. Episclera

2. Stroma

3. Lamina fusca

The _____ is deeper than Tenon’s capsule.

Episclera

What supplies the episclera?

Anterior ciliary arteries (e.g. superficial capillary network and deep capillary network)

What is the scleral spur?

Circumferential collagen bundles that form a ring that extends from the inner sclera.

What does the anterior and posterior of the scleral spur serve as?

• Anteriorly: site of attachment of trabecular meshwork

• Posteriorly: site of origin of ciliary body muscle

What structure does the anterior scleral foramen house?

• Cornea

• Limbus / corneoscleral junction

What structure does the posterior scleral foramen house?

Optic nerve

What is the weakest region of the sclera?

Lamina cribrosa

What is the lamina cribrosa?

It is the network of interwoven collagen fibrils bridging the posterior sclera foramen.

List vessels and nerves that pass through the anterior, posterior and equator of the scleral emissary canals.

• Anteriorly: Anterior ciliary arteries and Episcleral vessel branches

• Near equator: Vortex veins

• Posteriorly: Long / short posterior ciliary arteries and ciliary nerves

The sensory innervation of the sclera is innervated by branches of the _______ nerve.

Nasociliary nerve (branch of ophthalmic nerve)

What is the Axenfeld loop?

Long ciliary nerve branch that reaches scleral surface.

What innervates the posterior sclera? What about the rest of the sclera?

• Posterior: short ciliary nerves

• Rest of sclera: long ciliary nerves

What determines scleral opacity?

1. Organization of collagen fibrils

2. Size of collagen fibrils

3. Hydration state