Eye Development

Question 1

Critical period for eye development:

Answer 1

Wk 4 - 8

Question 2

3 embryonic sources for the eye

Answer 2

Neuroectoderm
Surface ectoderm
Mesoderm/neural crest (mesenchyme = mixture of both)

Question 3

Eye precursor:

Answer 3

Prosencephalon (optic sulcus, optic vesicle, optic stalk, optic fissure)
-neuroectoderm

Question 4

Draw the prosencephalon right before eye development

Answer 4

Refer to drawings

Question 5

Prosencephalon will divide into …

Answer 5

Telencephalon (brain proper) and Diencephalon (thalamuses and eye)

Question 6

Describe the development of the optic cup:

When does this begin?

Answer 6

Begins at wk 4
Inner and outer layer form from the optic stalk at the lens pit > invaginate in > lens vesicle grows inward > optic fissure covers the optic stalk
Hyaloid artery and vein (from mesoderm) are incorporated in

Question 7

Draw the development of the optic cup

Answer 7

Refer to drawings

Question 8

Inner and outer layer of the optic cup will give rise to…

Derived from…

Answer 8

Retina

Neuroectoderm

Question 9

What structures are derived from neuroectoderm?

Answer 9

Retina (neural/inner and pigmented/outer retina)
Iris (epithelium, smooth muscles of the iris (only muscles coming from ectoderm)
Ciliary body epithelium)

Question 10

The stroma of the iris comes from …

Ciliary muscle of the ciliary body comes from…

Answer 10

Mesenchyme (mesoderm and neural crest)

Mesenchyme (mesoderm and neural crest)

Question 11

Detachment of retina:

Answer 11

Separation of the pigmented and neural retina

Usually seen in Down’s and Marfans

Question 12

Aniridia:

Answer 12

Pax6 mutation
Lack of iris
Defect results from: arrest of development at rim of optic cup at 8th week
Associated with glaucoma, cataracts and other abnormalities

Question 13

How do lens develop?

Answer 13

Optic cup grows out > touches the surface ectoderm and induces it to develop the lens placode > lens placode thickens > invaginates and forms the lens pit > forms the lens vesicle > migrate around the space of optic cup

Question 14

Why is lens clear?

Answer 14

Due to anterior lens epithelium, primary and secondary lens fibers (all from surface ectoderm)

Question 15

Epithelium of the cornea is derived from…

Stroma of cornea is derived from….

Answer 15

Surface ectoderm

Mesenchyme (mesoderm and neural crest)

Question 16

Congenital cataracts :
Cause
Clinical

Answer 16

Genetics, rubella (esp between wk 4-7), radiation or congenital galactosemia (galactose buildup, appears 2-3 weeks post birth)
Cloudiness is only at the lens at the center of pupil

Question 17

Draw the derivatives of mesenchyme and neural crest:

Answer 17

Refer to drawings

Question 18

Which structures are derived from mesenchyme:

Answer 18

Outer layer of the sclera
Stroma of cornea
Pupillary membrane

Question 19

What structures are derived from solely neural crest?

Answer 19

Choroid Inner layer is pia and arachnoid

Question 20

When does the pupillary membrane degenerate?

Answer 20

6 - 8 months in utero

Question 21

At anterior chamber, what happens to aqueous humor?

At posterior chamber, what happens to aqueous humor?

Answer 21

• resorbed by scleral venous sinus
• secreted by ciliary epithelium

So it flows from posterior chamber through pupil into the anterior chambe

Question 22

Vitreous humor is made by …

Aqueous humor is made by …

Answer 22

Choroid

Ciliary body, protective and sends nutrients to lens since blood supply is limited to retina

Question 23

Ciliary epithelium is derived from ….

Scleral venous sinus is derived from…

Answer 23

Neuroectoderm

Mesenchyme

Question 24

Congenital glaucoma

Answer 24

Results from: abnormal development of the canal of schlemm. Stems from elevated intraocular pressure from clogged Schlemm’s canal
Causes: genetics, mutations in CYP1B1, rubella infection

Question 25

Which cell type do extra-ocular muscles come from?

Answer 25

Prechordal mesenchyme

Question 26

Blood supply of the developing eye:

Answer 26

Mainly the Hyaloid artery (from opthalmic a.) supplies the inner layer of optic cup, lens vesicle, mesenchyme
This develops into the central retinal artery. Plexus to the optic cup etc. will degenerate and final structure only supplies the retina

Question 27

Choroidal vessels

Answer 27

develop in the choroid during wk 15

Question 28

Hyaloid artery and choroidal vessels are derived from?

Answer 28

Mesenchyme

Question 29

Persistence of the hyaloid artery:

Answer 29

Distal part of the structure persists when it should degenerate, floating structure in the back of the eye
Eye is usually microphthalmic (small eye) in most cases

Question 30

Retinal ganglion cells

Answer 30

Light passes through both pigmented and neural layers of the retina to get to the ganglion cells
Neural layer has the rods/cones and ganglion cells

Question 31

Development of optic nerve:

Role of optic stalk

Answer 31

Optic stalk is NOT the optic nerve, but it provides pathway for the axons of the ganglion cells axons to get to the brain
Hyaloid artery is incorporated in the substance of the optic nerve (remember this is embedded in the optic nerve and covered by all meningeal layers)
Optic stalk will degenerate and leave the optic nerve

Question 32

Papilledema

Answer 32

• increased intracranial pressure slows venous return from retina, causing accumulation of the optic disc
• Edema occurs because the retinal vessels are covered by the meninges and lie in the extension of the subarachnoid space

Question 33

Coloboma:

Answer 33

Optic fissure fails to close leaving gap in the eye structures. Optic fissure is a notch in the optic cough so that needs to close to get the complete iris.
Unable to constrict with too much light. Can end up damaging the retina