MedBucket

Choroid is a part of the middle layer of the eye. More specifically, it is located between the outer and the inner eye layers. It has two sides: the inner and the outer one. The outer side is a bit prominent because of the presence of arteries and nerves. The inner side is smooth because it is the basis for the inner layer of the eye — the retina.

The choroid is comprised of four layers:

1. lamina suprachoroidea
2. lamina vasculosa
3. lamina choriocapillaris
4. lamina basalis

1. This layer is made out of 6-8 layers of lamelles which are comprised of pigment cells and a lot of elastic fibers. Lamelles are covered from both sides with endothelium. These lamelles form spaces which are filled with lymph — these spaces are called spatium suprachoroidale.

2. This layer is made out of branches given by ciliary arteries (arteriae ciliares posteriores breves and arteriae ciliares posteriores longae) and choroid veins (venae choroideae). All these elements are drowned in binder tissue with a lot of pigment cells. The amount of pigment cells varies from person to person. If we perform an ophtalmoscopic exam on a person with tiny amounts of pigment cells, we will be able to see clearly the eye’s bottom (fundus oculi) in red color (caused by blood vessels). On the other hand, by performing the same exam on a person with big amounts of pigment cells, we will see a darkish eye’s bottom. This is called the fundus tabulatus.

3. This layer is filled with capillaries, both arterial and venous. These capillaries are very wide, and thus remind of sinusoids. This layer is in charge of feeding the inner layer of the eye, and that’s why it’s very advanced in the area of macula lutea.

4. This is a very thin membrane whose inner side is very smooth because it is the basis for the inner layer of the eye.

Choroid doesn’t have lymph vessels (except for the aforementioned lymph spaces). Innervation origins from the ciliary nerves.