Embryology of the Eye Flashcards
What is the eye an extension of?
The brain
What does the brain develop from?
The neural tube
What do the signals sent from the notochord induce?
Ectodermal cell thickening
How does the neural plate form a tube?
- Development of the neural plate leads to the middle sinking down with a crest either side.
- The 2 crests come closer together until they meet and form a tube
Where is the neural tube situated?
Dorsal end of the embryo
What is the cranial end of the neural tube divided into?
A number of vesicles
What does each vesicle form?
A different part of the brain
Which vesicle do the optic vesicle project laterally from?
Diencephalic vesicle
How do the optic vesicles grow?
Outward and laterally
Placode
Embryological thickening
What happens when the optic vesicles reach the limits of the surface ectoderm?
It will send out signals which stimulates the surface epithelium to thicken forming the lens placode
How is the optic cup formed?
- The lens placode will start to invaginate (push inwards)
- The optic vesicle itself will be pushed inwards
- This leads to the formation of 2 layers known as the optic cup
How is the optic cup connected to the neural tube?
By a stalk
What do the 2 layers of the optic cup form?
The layers of the retina
Mesenchyme
Embryonic tissue
How are the choroid and sclera formed?
The mesenchyme around the optic cup condenses
How is the crystalline lens formed?
The lens vesicle which has gone inwards loses its connection to the surface epithelium to form the crystalline lens
What does the surface epithelium form?
Cornea and the front parts of the sclera
How are the eyelids formed?
At a later stage some of the tissue folds over to form the eyelids
How is the choroid fissure formed?
When the lens vesicle is growing and as it is folding inwards there is a blood vessel that grows into it. This creates a little groove in the developing retina and optic nerve creating the choroid fissure.
What happens to the choroid fissure?
In time the fissure closes off
How is the blood supply to the retina formed?
The choroid fissure closes off but the blood vessels remain within the substance of the optic nerve and becomes the central retina artery and goes to supply the surface of the retina
How many layers does the retina have histologically?
10
What is the 10th layer of the optic cup formed from?
Outer layer of the optic cup
What is there between layers 1-9 of the retina and the 10th layer?
Potential space
How can retinal detachment occur?
- Can occur as a consequence of many diseases
- In most cases it occurs as a result of fluid entering the potential space separating the inner 9 layers from the outer 10th layer
What does the surface ectoderm form?
- Eyelids
- Conjunctiva
- Corneal epithelium
What does the mesenchyme form?
- Choroid
- Stroma of the cornea
- Sclera
- Extraocular muscles
What do the lens fibres form from?
Epithelium of lens vesicle and later lose their nuclei
What is mesenchyme derived from?
Mesoderm and neural crest cells
