Layers of the Sclera, Function, Blood Supply, and Innervation

Question 1

3 layers of the sclera

Answer 1

Outer — inner

Conj 
Tenons
Episclera
Sclera
Lamina Fusca

Question 2

Transverse, vertical and anteroposterior diameters of the sclera for an emmetropic human adult eye

Answer 2

Transverse- 24mm
Vertical- 24mm
Anteroposterior- 22-24.5mm

**Would be longer for myope and shorter for hyperope.

Question 3

Where is the sclera the thickest, and where is it the thinnest?

Answer 3

Sclera is the thickest posteriorly near the optic nerve at 1-1.35mm. It decreases in thickness gradually as it approaches the equator of the globe.

It is the THINNEST under the rectus muscle just before insertion at 0.3mm. At the insertion site of the muscle, it increases in thickness. Continues to increase in thickness towards the limbus.

Question 4

Sclera has a (greater/lesser) radius of curvature compared to the cornea

Answer 4

Greater. 12.5mm

Question 5

Anteriorly to posteriorly, the sclera extends from

Answer 5

Limbus to limbus anteriorly to the ON and will merge with the dural sheath posteriorly.

Question 6

Episclera characteristics

Answer 6

Composed of loose connective tissue (fibroblasts, collagenous fibers, ground substance) with MANY BLOOD VESSELS. Highly vascularized.

Thin, outermost region of the sclera.

Question 7

Sclera is composed of ___

Answer 7

Thick dense connective tissue (fibroblasts, collagenous fibers- most commonly type 1, elastic fibers, ground substance.)

Question 8

Most predominant type of collage in sclera and what is the arrangement

Answer 8

Type 1. Arrangement contributes to strength and white/opaque color- the diameter and spacing between the fibers vary. Ex: The diameter of the fibers can be between 25-230nm.

The collagen fibers are grouped into bundles that are arranged in lamellae. The outer lamellae course parallel to the surface and the inner courses in all directions.

The most inner portion of the sclera contains fibers that are circular arranged, forming a ring called the scleral spur.

Question 9

Scleral spur

Answer 9

Collagen fibers found deepest in the sclera that are arranged in circularly, forming a ring.

Longitudinal ciliary muscle fibers attach to the posterior border of the scleral spur.

Question 10

Where is elastin found in the sclera?

Answer 10

Abundant deep in the sclera, especially near the rectus muscle insertions and more posteriorly.

Question 11

Why would the sclera appear blue or yellow?

Answer 11

If sclera stroma is thin, it may appear BLUE. This could be due to age, infants with low levels of collagen, or people with collagen disease.

If sclera is YELLOW, this may indicate fatty deposit build up or metabolic waste build up due to liver disease (Jaundice)

Question 12

Lamina Fusca

Answer 12

Innermost aspect of the sclera, adjacent to the choroid. This is modified scleral stroma that contains a large number of melanocytes that migrate from the chorioid. This gives the tissue a brown color.

Question 13

Anterior apertures of the sclera

Answer 13

Anterior apertures are near the recti muscle insertions.
Includes holes for anterior ciliary arteries and veins(branch of the muscular artery).

Long ciliary nerves may also enter the aperture and exit on their way to innervate the cornea. This is called an axenfeld loop and may be surrounded by pigment.

Question 14

Axenfeld loop

Answer 14

When long ciliary nerves are on the way to the cornea, and take a detour and exit the globe through the anterior apertures and turn right around, re-enter, and go to the cornea. May be surrounded by pigment.

Question 15

Middle apertures

Answer 15

Found 4mm posterior to the equator in all four quadrants. Serve as holes for vortex veins to exit through. Vortex veins drain blood from the retina and can be observed through fundus imaging.

Question 16

Posterior apertures

Answer 16

Located AROUND the scleral canal (posterior foramen), which surrounds the optic nerve.

Holes for short posterior ciliary arteries, long posterior ciliary arteries, short ciliary nerves, and long ciliary nerves.

Question 17

Anterior foramen

Answer 17

Area occupied by the cornea

Question 18

Posterior foramen (scleral canal)

Answer 18

Hole for central retinal artery, central retinal vein and optic nerve fibers. Transverse scleral fibers form a fenestrated scaffold called the lamina cribrosa, which is the weakest area of the sclera.

Question 19

Lamina cribrosa

Answer 19

Fenestrated sclera found in the posterior foramen (Scleral canal). A weak area of the sclera that allows passage of central retinal artery and vein, and optic nerve fibers.

Question 20

The episceral arterial circle supplies the

Answer 20

Episclera, sclera, and lamina fascia.

Question 21

Is the sclera stroma vascular or avascular?

Answer 21

Avascular

Question 22

Where do the episcleral veins drain into?

Answer 22

The superior and inferior ophthalmic veins

Question 23

What branches off the nasociliary nerve (V1) to supply the anterior sclera and posterior sclera?

Answer 23

Long ciliary nerves supply anterior sclera
Short ciliary nerves supply the posterior sclera

These nerves travel though posterior apertures to reach the sclera