Embryology of the Eye

Question 1

What is the eye an extension of?

Answer 1

The brain

Question 2

What does the brain develop from?

Answer 2

The neural tube

Question 3

What do the signals sent from the notochord induce?

Answer 3

Ectodermal cell thickening

Question 4

How does the neural plate form a tube?

Answer 4

• 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

Question 5

Where is the neural tube situated?

Answer 5

Dorsal end of the embryo

Question 6

What is the cranial end of the neural tube divided into?

Answer 6

A number of vesicles

Question 7

What does each vesicle form?

Answer 7

A different part of the brain

Question 8

Which vesicle do the optic vesicle project laterally from?

Answer 8

Diencephalic vesicle

Question 9

How do the optic vesicles grow?

Answer 9

Outward and laterally

Question 10

Placode

Answer 10

Embryological thickening

Question 11

What happens when the optic vesicles reach the limits of the surface ectoderm?

Answer 11

It will send out signals which stimulates the surface epithelium to thicken forming the lens placode

Question 12

How is the optic cup formed?

Answer 12

• 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

Question 13

How is the optic cup connected to the neural tube?

Answer 13

By a stalk

Question 14

What do the 2 layers of the optic cup form?

Answer 14

The layers of the retina

Question 15

Mesenchyme

Answer 15

Embryonic tissue

Question 16

How are the choroid and sclera formed?

Answer 16

The mesenchyme around the optic cup condenses

Question 17

How is the crystalline lens formed?

Answer 17

The lens vesicle which has gone inwards loses its connection to the surface epithelium to form the crystalline lens

Question 18

What does the surface epithelium form?

Answer 18

Cornea and the front parts of the sclera

Question 19

How are the eyelids formed?

Answer 19

At a later stage some of the tissue folds over to form the eyelids

Question 20

How is the choroid fissure formed?

Answer 20

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.

Question 21

What happens to the choroid fissure?

Answer 21

In time the fissure closes off

Question 22

How is the blood supply to the retina formed?

Answer 22

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

Question 23

How many layers does the retina have histologically?

Answer 23

10

Question 24

What is the 10th layer of the optic cup formed from?

Answer 24

Outer layer of the optic cup

Question 25

What is there between layers 1-9 of the retina and the 10th layer?

Answer 25

Potential space

Question 26

How can retinal detachment occur?

Answer 26

• 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

Question 27

What does the surface ectoderm form?

Answer 27

• Eyelids
• Conjunctiva
• Corneal epithelium

Question 28

What does the mesenchyme form?

Answer 28

• Choroid
• Stroma of the cornea
• Sclera
• Extraocular muscles

Question 29

What do the lens fibres form from?

Answer 29

Epithelium of lens vesicle and later lose their nuclei

Question 30

What is mesenchyme derived from?

Answer 30

Mesoderm and neural crest cells