Ocular Development

Question 1

Which 2 layers does the eye develop from

Answer 1

Ectoderm (surface ectoderm, neuroectoderm and neural crest cells)
Mesoderm

Question 2

What is Gastrulation

Answer 2

development from a single-layered blastula to a multilayered gastrula), 3 germ layers form in all animal embryos: ectoderm (superficial layer of cells), mesoderm (middle layer), and endoderm (inner layer)

Question 3

What are neural crest cells

Answer 3

transient migratory stem cells that can form tissues with ectodermal and mesodermal characteristics

Question 4

When does the optic primordium appear

Answer 4

Day 22

Question 5

Derivatives of Neuroectodermal tissue

Answer 5

Ciliary body epithelium (pigmented and nonpigmented)
Iris sphincter and dilator muscles
Neurosensory retina
Optic nerve,axons and glia
RPE
Vitreous

Question 6

Derivates of Neural Crest Cells

Answer 6

Bones: midline and inferior orbital bones, parts of orbital roof and lateral rim
Cartilage
Choroid/iris stroma
Ciliary ganglion
Connective tissue of orbit
Corneal stroma and endothelium
EOM sheaths and tendons
Orbital fat
Melanocytes (uveal and epithelial)
Meningeal sheaths of ON
Schwann cells of ciliary nerves
Sclera (except temporal sclera)
Trabecular meshwork
Vitreous
Vasculature: muscle and connective tissue sheaths of ocular and orbital vessels

Question 7

Derivatives of Surface ectoderm

Answer 7

Corneal epithelium
Conjunctival epithelium
Epithelium, glands, cilia of skin of eyelids, and caruncle Lacrimal drainage system
Lacrimal gland (also from neural crest)
Lens
Vitreous

Question 8

Derivatives of Mesoderm

Answer 8

Choroid
Ciliary body
Extraocular muscle fibers
Fat (also see Neural crest cells)
Iris stroma
Temporal sclera (also see Neural crest cells) Vascular endothelium
Vitreous (also see Neural crest cells)

Question 9

How does the optic cup form

Answer 9

Once the optic vesicle touches the inner aspect of the surface ectoderm, the vesicle invaginates to form a bilayered optic cup. (Note that the embryologic optic cup is not the same as the anatomical optic cup of the optic nerve head.)The inner layer forms the neural retina, and the outer layer forms the retinal pigment epithelium (RPE)

Question 10

How do colobomas form

Answer 10

The invagination of the optic cup occurs asymmetrically (Fig 4-7), with a ventral fissure that facilitates entry of mesodermal and neural crest cells. The fissure closes at its center first and then “zips” both anteriorly and posteriorly. Failure of fissure closure leads to a colo- boma.

Question 11

Which coloboma is most common

Answer 11

anterior colobomas are the most common (they cause iris and occasionally anterior scleral defects); central colobomas are the least common; and posterior colobomas occur with a frequency somewhere in between (they give rise to optic nerve head, retinal, and choroidal defects). The location of fissure closure correlates with the inferonasal quadrant, which is where colobomas are clinically found.

Question 12

What are some lenticular opacity and abnormal development of the eye

Answer 12

Development of the lens vesicle is supported by a branching network of vessels, derived from the hyaloid artery, known as the tunica vasculosa lentis. Failure of this tissue to regress can lead to conditions ranging from pupillary membranes that are seen on routine slit-lamp examination, to a malformation called persistent fetal vasculature (also called persistent hyper- plastic primary vitreous)

Question 13

What does the hyaloid artery become

Answer 13

It is retained within the optic nerve and eventually becomes the central retinal artery

Question 14

What is the only pigmented tissue in the body not derived from neural crest cells

Answer 14

RPE

Question 15

What are the remnants of the primary vitreous

Answer 15

Cloquet canal and its anterior extension, the hyaloideo- capsular ligament (also known as ligament of Weiger).

Question 16

Congenital cranial dysinnervation disorders

Answer 16

Duane re- traction syndrome, Marcus Gunn jaw-winking syndrome, Möbius syndrome, and con- genital fibrosis of the extraocular muscles. Genetic studies have identified mutations in genes for neuron biology and axon guidance (eg, KIF21A, PHOX2A, TUBB3) that cause these EOM syndromes.

Question 17

Blueprint for embryonic program

Answer 17

homeobox genes (HOX).
The function of HOX genes as master regulators arises from the ability of these genes to regulate expression of downstream genes through homeodomain binding to DNA pro- moter sequences, wherein they act as switches of gene transcription. Each set of switches drives a particular cell fate, and transcriptional cascades of these switches lead to the development of different tissues and organs.

Question 18

Features of the PAX6 gene

Answer 18

It appears to be a master switch for eye development. The PAX6 transcription factor is expressed in a band in the anterior neural plate, very early in the primordial eye field, and ectopic expression of PAX6 can lead to ectopic eyes and aniridia, Peters anomaly, coloboma, and microphthalmia.

Question 19

Growth factors for ocular development

Answer 19

The most important of these factors include retinoic acid (RA), Wnt, fibroblast growth factors (FGFs), the hedgehog family members Shh and Ihh, and insulin-like growth factor (IGF)

Question 20

Group 1 ligands

Answer 20

Group 1 ligands interact with intracellular receptors that directly regulate gene expression (eg, RA)

Question 21

Group 2 ligands

Answer 21

Group 2 ligands interact with cell-surface receptors that initiate an intracellular signalling cascade (eg, Wnt, FGF), often involving protein phosphorylation cascades, to eventually affect gene expression and intracellular remodelling (eg, cytoskeleton), cell motility, protein trafficking, and other processes.