The ciliar body is a part of the middle layer of the eye. It is located between iris and ora serrata. Its external side is pretty smooth, and it leans onto sclera, especially on the front side. The internal side is pretty creased, and divided into two zones — orbiculus ciliars, which is closer to the equator and has smaller creases (plicae orbiculares) and corona ciliaris, which is more to the front and has bigger creases (processus ciliares majores). Between these ciliary creases there are ciliary notches called sulci ciliares. In them, there are fibers called zonula ciliaris, which hold the lens in its position.
The ciliar body is built similarly to choroid — it contains two parts. The first one (pars vascularis) is a lot of binder tissue full of blood vessels and pigment cells, while the second one (to the outside) is the ciliary muscle (musculus ciliaris).
The ciliary muscle is comprised of three parts:
1. Fibrae meridionales
2. Fibrae radiales
3. Fibrae circulares
When the ciliary muscle gets contracted, it pulls the choroid to the front, thus making the zonula ciliaris to loosen the lens. The lens bulges and the eye becomes accommodated for nearness. Contrary to that, when the ciliary muscle gets relaxed, it pulls the choroid to the back, thus making the zonula ciliras to tighten the lens. The lens excavates and the eye becomes accommodated for distance.
The innervation comes from the ciliary nerves through the ganglion ciliare, which form the plexus gangliosus ciliaris around the muscle.
Iris is a part of the middle layer of the eye. It has its anterior and a posterior side, a border and an opening called pupilla (pupil).
The anterior side of iris (facies anterior iridis) is free, slightly convex because of the lens which is located behind it. Where the two lateral and one medial third meet, there is a ledge called iridal ledge. The iridial ledge divids iris into two parts — the bigger called anulus irids major and a smaller called anulus iridis minor. On the bigger one there are circular creases, while the smaller one contains cavities. The cavities are called the iridial crypts.
The posterior side of iris is slightly concave and is touching the frontal side of the lens. These two aren’t glued to one another — they are just rubbing onto each other, thus allowing the eye water to pass from the camera bulbi posterior to the camera bulbi anterior. There are pathological cases when these two structures get glued to one another, and that is called the secclusio pupillae. This can cause permanent blindness if not operated immediately.
Iris is made out of binder tissue and smooth muscle fibers. It is comprised of four layers:
1. Endothelium camerae anterioris
2. Stroma
3. Stratum musculare
4. the iridial part of the inner layer of the eye
1. This layer is actually covering the stroma on the front side. It is only present in children — later it gets ruptured and disappears.
2. This layer is the main part of iris. It is made out of binder tissue filled with pigment and non-pigment cells. The presence or non-presence of pigment cells in this layer determins the color of people’s eyes. People who have a lot of pigment cells in this layer have black or brown eyes. People who have small amounts of pigment cells have green eyes. People who have very small amounts of pigment cells in this layer have blue eyes. Finally, people who don’t have any pigment cells in this layer have specific dark-blue eyes.
3. This layer consists of two muscles: musculus sphincter pupillae and musculus dilatator pupillae. This first one tightens the pupil, while the second one relaxes it.
4. This layer origins from the brain, and is made out of 3-4 layers of epithelial cells.
The innervation origins from the plexus ganglious ciliaris — its branches head towards the pupil and produce the plexus pupillaris around it.
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.
The middle layer of the eye (tunica media bulbi) is a layer located between the out and the inner layer of the eye. Its primary function is feeding the whole eye, while its secondary function is eye accommodation.
This layer is comprised of three main parts: choroid, iris and ciliary body.
Cornea is a part of the outer layer of the eye. Its main characteristic is its transparency. Cornea has two sides, the outer (anterior) and the inner (posterior) one, and a border. The outer side is convex and smooth, covered with conjunctiva. The inner side is concave — more than the outer side is convex, causing the cornea to be differently thick. The wider parts are thicker (1.1mm), while the central parts are thinner (0.8mm). Cornea’s border gets between the lips of sclera, thus creating a formation called limbus corneae.
The cornea is made out of five layers:
1. epithelium anterius cornae
2. lamina limitans anterior
3. substantia propria corneae
4. lamina limitans posterior
5. endothelium camerae anterioris
1. The first layer is a classic epithelium made out of five layers of cells. The bottom layer is consisted of cylindrical cells, which form and produce the upper layers.
2. This membrane is a very thin membrane which is located between the epithelium and the substantia propria. It’s homogeneous and it provides the next layer with a smooth basis.
3. Substantia propria corneae is made out of bundles of binder fibrils, which form lamelles. The fibrils located within one lamelle cross each other (90° angle) with fibrils in other lamelles. Between the fibrils and the lamelles there are various spaces filled with corneal cells and lymph.
4. This membrane is a very thin, but elastic membrane. It is very strong and easily resists pathological processes.
5. This layer is a typically simple endothelium with huge nucleuses. It prevents the eye water to pass in the substantia propria.
Cornea doesn’t have any blood vessels — they are located on a peripheral location. If there were blood vessels in cornea, the light couldn’t get through. The innervation is prolific. The nerves come from the ciliary nerves and form a plexus near the sinus venosus sclerae. Branches of that plexus go to the inner parts and form two other plexuses — plexus cornealis profundus and plexus subepithelialis. The latter’s branches form the plexus interepithelialis.