Embryology of the Eye

Question 1

What is the origin of the eye growth?

Answer 1

It’s an extension of the Brian, and so forms as an extension of the developing brain -> neuralectodermal in origin

Question 2

What are the three steps in development of the neural tube?

Answer 2

1. Notochord signals trilaminar layers to thicken and form neural plate
2. Increase in neural plate causes it to sink down and two ends join to form a tube
3. Neural tube is on dorsal end of embryo

Question 3

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

Answer 3

Vesicles, with each vesicle forming a different part of the brain

Question 4

From which vesicles do the eye form?

Answer 4

The diencephalic vesicle

Question 5

How do the eyes form from the diencephalic vesicle?

Answer 5

1. Lateral projections from diencephalic part of neural tube -> optic vesicles
2. Once it reaches limits of of ectoderm, it send signals to surface ectoderm cells to thicken -> lens placode
3. Len placode begins to invaginate, causing optic vesicles to become concave –> optic cup with stalk that connects it to the neural tube

Question 6

What does the stalk that is connected to the optic cup form?

Answer 6

The optic nerve

Question 7

What are the two layers of the optic cup?

Answer 7

Endoderm and ectoderm (lens placode)

Question 8

What do the two layers of the optic cup eventually form?

Answer 8

Retina

Question 9

What forms the choroid and sclera?

Answer 9

Mesenchyme

Question 10

How does the crystalline lens form?

Answer 10

Lens vesicle loses connection with surface ectoderm

Question 11

What does the surface epithelium form?

Answer 11

Cornea and front parts of the sclera and eyelids

Question 12

What is the choroid fissure?

Answer 12

When the lens vesicle is growing and folding inwards, there’s a blood vessel that grows into it and creates the groove in the developing retina and the optic nerve

Question 13

What happens to the choroid fissure?

Answer 13

Closes off but the blood vessels remain within the substance of the optic nerve and become the central retinal artery

Question 14

How do the different layers of the retina form?

Answer 14

Optic cup -> forms 10th (outer layer) and 9th layer

Question 15

What is the clinical significance of the 10th and 9th layers of the retina?

Answer 15

Both forming from the optic cup leaves a potential space between the 9 inner layer and 10th outer layer – clinically, retinal detachment can occur due to diseases which cause fluid to enter the potential space causing layers to separate

Question 16

What does the surface ectoderm form?

Answer 16

Eyelids
Conjunctiva
Corneal epithelium

Question 17

What does the mesenchyme form?

Answer 17

Choroid
Stoma of cornea
Sclera
Extraocular muscles