Eye Development Flashcards
Critical period for eye development:
Wk 4 - 8
3 embryonic sources for the eye
Neuroectoderm
Surface ectoderm
Mesoderm/neural crest (mesenchyme = mixture of both)
Eye precursor:
Prosencephalon (optic sulcus, optic vesicle, optic stalk, optic fissure)
-neuroectoderm
Draw the prosencephalon right before eye development
Refer to drawings
Prosencephalon will divide into …
Telencephalon (brain proper) and Diencephalon (thalamuses and eye)
Describe the development of the optic cup:
When does this begin?
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
Draw the development of the optic cup
Refer to drawings
Inner and outer layer of the optic cup will give rise to…
Derived from…
Retina
Neuroectoderm
What structures are derived from neuroectoderm?
Retina (neural/inner and pigmented/outer retina)
Iris (epithelium, smooth muscles of the iris (only muscles coming from ectoderm)
Ciliary body epithelium)
The stroma of the iris comes from …
Ciliary muscle of the ciliary body comes from…
Mesenchyme (mesoderm and neural crest)
Mesenchyme (mesoderm and neural crest)
Detachment of retina:
Separation of the pigmented and neural retina
Usually seen in Down’s and Marfans
Aniridia:
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
How do lens develop?
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
Why is lens clear?
Due to anterior lens epithelium, primary and secondary lens fibers (all from surface ectoderm)
Epithelium of the cornea is derived from…
Stroma of cornea is derived from….
Surface ectoderm
Mesenchyme (mesoderm and neural crest)
Congenital cataracts :
Cause
Clinical
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
Draw the derivatives of mesenchyme and neural crest:
Refer to drawings
Which structures are derived from mesenchyme:
Outer layer of the sclera
Stroma of cornea
Pupillary membrane
What structures are derived from solely neural crest?
Choroid Inner layer is pia and arachnoid
When does the pupillary membrane degenerate?
6 - 8 months in utero
At anterior chamber, what happens to aqueous humor?
At posterior chamber, what happens to aqueous humor?
- resorbed by scleral venous sinus
- secreted by ciliary epithelium
So it flows from posterior chamber through pupil into the anterior chambe
Vitreous humor is made by …
Aqueous humor is made by …
Choroid
Ciliary body, protective and sends nutrients to lens since blood supply is limited to retina
Ciliary epithelium is derived from ….
Scleral venous sinus is derived from…
Neuroectoderm
Mesenchyme
Congenital glaucoma
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
Which cell type do extra-ocular muscles come from?
Prechordal mesenchyme
Blood supply of the developing eye:
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
Choroidal vessels
develop in the choroid during wk 15
Hyaloid artery and choroidal vessels are derived from?
Mesenchyme
Persistence of the hyaloid artery:
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
Retinal ganglion cells
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
Development of optic nerve:
Role of optic stalk
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
Papilledema
- 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
Coloboma:
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
