Week 9: Uvea 3

Question 1

What is the choroid?

Answer 1

-Lines the sclera from the ora serrata to the edge of optic disc.
-Thickness of about 0.2mm.
> Vascular structure of the choroid provides a
route for metabolites to the anterior eye, and
nutrition to and removing waste from the retinal receptors.
> It is heavily pigmented, with melanin-containing cells giving it a brown colour for light absorption (any photons pass through retina aren’t picked up by photoreceptors don’t bounce off structures like the sclera but get absorbed by pigment within choroid.

Question 2

What are the layers within the choroid?

Answer 2

• Suprachoroid (outside)
• Stroma
• Choriocapillaris
• Basal Lamina (Bruch’s Membrane) (inside)

Question 3

What is the suprachoriod?

Answer 3

> A transition zone between the choroid and sclera
Is about 30µm thick.
Consists of collagen fibres continuous with those of the sclera and melanocytes and fibroblasts (unlike sclera)
- Carries nerves and blood vessels to and from the anterior uvea
- The nerves that terminate in the choroid are derived from the short posterior ciliary nerves.

Question 4

What is the stroma?

Answer 4

2. Stroma:
   > Most of bulk thickness of choroid.
   > Pigmented layer consisting principally of blood vessels.
   > Between the vessels are melanocytes with pigment and fibroblasts with some collagen and ground substance (scaffolding of matrix).
   > Macrophages (phagocytosis cells often filled with pigment) and lymphocytes (T+B cells) are also present.
   > Blood vessels in this layer are sometimes divided an external layer of large vessels: (Haller’s layer), and an internal layer of smaller vessels (Sattler’s layer).

Question 5

What is the choriocapillaris?

Answer 5

> A fine layer of capillaries with an unusual organisation …..
a) Capillaries lie in a single plane against the internal limiting lamina of the choroid, are not
distributed throughout the thickness of the
tissue like normal…
b) Capillaries are unusually wide, about 30um. (Provides nutrients & removing waste from retina)
Fine collagen fibres are present between the capillaries together with fibroblasts and umnyelinated nerve fibres.
The choriocapillaris is free of pigment (unlike all other structures in choriod).

Question 6

What is the basal lamina (Bruch’s membrane)?

Answer 6

> Is layered with an outer elastic and an inner cuticular lamina
The cuticular lamina is about 2µm thick, and consists of the basement membrane of the retinal pigment epithelium and a layer of
collagen.
External to this is a layer of elastin, and then a second layer of collagen and then the basement membrane of the endothelial cells of the capillaries of the choriocapillaris.
With ageing the cuticular layer of Bruch’s membrane may thicken to form mounds called drusen, which contain granular material believed to be secreted by the retina pigment epithelial cells.