Chapter 4: Ocular Development Flashcards Preview

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Flashcards in Chapter 4: Ocular Development Deck (39):

How many germ layers are present during gastrulation?

- Ectoderm
- Mesoderm
- Endoderm


What germ layers do the eyes and orbit develop from?

The eyes and orbit develop from all three germ layers, with neural crest cells making a substantial contribution


What is the earliest sign of ocular development?

Formation of the Lens Placode is the first sign of ocular development


What is the Lens Placode?

small surface ectoderm thickenings on both sides of the developing head


What are optic vesicles? When during embryogenesis do they develop?

optic pits that fill up to form pouches that are derived from ectoderm. They connect to the forebrain via a narrow neck. They develop around the same time as the lens placode.


What is the optic cup?

bi-layered invagination of the optic vesicles that occurs after they come into contact with the surface ectoderm


What are the two layers of the optic cup?

the inner layer, which becomes the neurosensory retina

the outer layer, which becomes the RPE


How does the Lens begin to form?

As the optic cup forms, the surface ectoderm begins to invaginate


How does lens formation contribute to development of the anterior segment?

As the surface ectoderm is invaginating, the area b.w the optic cup and surface ectoderm is invaded by migrating mesodermal and neural crest cells


What are the steps in Lens Formation?

Lens Plate= proliferation of surface ectoderm
Lens Pit= inward invagination of lens plate
Lens Vesicle= Pit deepens, closes, and detaches from surface


What is the Lens Vesicle?

a single layered structure composed of cuboidal cells surrounding a large lumen

sits in the optic cup


Describe the formation of the primary lens fibers

Posterior Lens epithelium proliferates, elongates, and fills in the optic vesicle

Called the embryonal nucleus


How does the lens capsule form?

the remaining epithelial cells form the lens capsule, which is composed of type IV collagen


What do the zonular fibers develop from?

they develop as a part of the vitreous and ciliary body (via mainly ectomesenchymal cells)


What does the cornea develop from?

Corneal epithelium develops from surface ectoderm, and the stroma/endothelium develop from neural crest derived ectomesenchymal cells


What cell layers does the Uvea develop from?

Develops from a combination of neural ectoderm, mesoderm, and neural crest cells

Neural Crest cells--pigmented epithelial components

Mesoderm--spincter and dilator muscles, non-pigmented parts of the uvea (i.e. iris stroma and ciliary muscle)


What are the initial two layers involved in retinal development?

Neural retina forms from the inner layer of the optic cup

RPE forms from the outer layer of the optic cup


What germ layers are involved in formation of the vitreous?

Neural Ectoderm-- contribute to primary vitreous CT fibers
Mesoderm--hyaloid vasculature


Describe the formation of the primary vitreous?

Forms a central conical structure that contains the hyaloid vasculature and is surrounded by secondary vitreous


What is the significant of the Neural Retina Leucine Zipper (Nrl)?

is a transcription factor of the Maf subfamily, is an intrinsic regulator of Rod photoreceptor development


What are the first retinal cells to differentiate?

Ganglion Cells


When do the ILM/ELM of the retina form?

They form when cells cease proliferating and begin to differentiate


What is the only pigmented tissue in the body that does not form from neural crest cells?

RPE, which forms from proliferating pseudo stratified columnar epithelial cells


What structures does the optic nerve develop from?

the optic stalk, which is the narrow neck that connects the optic cup to the forebrain

is initially formed from neuroectodermal cells surrounded by neural crest cells


What germ layer/s form the Sclera?

formed from ectomesenchymal elements


When do the scleral spur and Tenons Capsule form?

They begin to form at the time of EOM insertion


Orbital development involves key contributions from which germ cell layers?

all of them--ectoderm, mesoderm, endoderm, and neural crest cells


What are the EOMs formed from?

They form from paraxial and prechordal mesoderm


Signals from what primitive ocular structure are necessary for proper migration of neural crest cells into the eye surrounding tissues?

The optic cup--interactions b.w optic cup, mesoderm, and neural crest cells are crucial for proper development and organization


What are some consequences of delayed innervation of EOM during development?

Innervation by the wrong nerve (occurs in Marcus Gunn Jaw Winking syndrome and Duane Syndrome)

Can also cause premature differentiation into CT (i.e. fibrosis)


When do bone/fat/cartilage/CT of the orbit develop? What do they develop from?

They develop by the 4th WGA from frontonasal and maxillary processes of neural crest cells that occupy the space around the optic cup


What is the only bone that isn't membranous during development? And what does it consist of?

The sphenoid bone is the only bone that isn't membranous, and its made of cartilage instead.


When does ossification of orbital bones occur during development?

Ossification occurs around the 3rd month of gestation


What does the upper eyelid develop from?

it develops from a proliferation of surface ectoderm in the region of the future outer can thus at 4-5 WGA


What type of cells eventually infiltrate the eyelids and form the palpebral muscles?

Mesodermal mesenchyme


When does the lacrimal gland begin to develop?

6-7 WGA


When does tear production by the lacrimal gland begin?

occurs >20 days after birth


What are homeobox genes?

they are the blueprint for embryonic program--serve as the main regulators of downstream development


What is the PAX6 gene? What is its significance relating to ocular development?

A homeobox gene that appears to be the master switch for ocular development