4 - Ocular Development Flashcards
2 feuillets embryonnaires impliqués dans le développement de l’oeil
Ectoderme
Mésoderme
Feuillet embryonnaire le plus impliqué dans le développement de l’oeil et ses sous-types
Most of the eye forms from different types of ectoderm:
* Surface ectoderm
* Neuroectoderm
* Neural crest cells (très grande contribution)
Causes de misactivation of genetic cascade (3)
- Gene mutations
- Oocyte abnormalities
- Exposure to teratogens
Conséquences de misactivation of genetic cascade (2)
Embryologic abnormalities that, in the most severe cases, are embryonic lethal or, in less severe cases, give rise to congenital abnormalities
Feuillets embryonnaires (et localisation)
- Ectoderm (superficial layer of cells)
- Mesoderm (middle layer)
- Endoderm (inner layer)
In addition, vertebrate embryos have an ectomesenchymal cell population that arises from neuroectoderm at the dorsal edge of the neural tube.
* These cells, known as neural crest cells, are transient migratory stem cells that can form tissues with ectodermal and mesodermal characteristics
D’où proviennent les neural crest cells?
In addition, vertebrate embryos have an ectomesenchymal cell population that arises from neuroectoderm at the dorsal edge of the neural tube.
- These cells, known as neural crest cells, are transient migratory stem cells that can form tissues with ectodermal and mesodermal characteristics.
Pourquoi les syndromes that arise from neural crest maldevelopment often involve the eye as well as facial, dental, and calvarial abnormalities (ex. Goldenhar syndrome)?
Neural crest cells make key contributions to eyes, orbital tissues, facial, dental, and cranial structures.
Nom de l’étape où il y a création des 3 feuillets embryonnaires durant le développement
Gastrulation
Que se passe-t-il a/n de l’ectoderm après l’étape de la gastrulation
Following gastrulation, the ectoderm separates into
* Surface ectoderm
* Neuroectoderm
À quel AG début le développement de l’oeil?
At 22 days, the optic primordium appears in neural folds.
Décrire les étapes de la neurulation
- Optic pits
- Optic vesicules
- Optic stalk (futur NO)
- Optic cup (invagination)
À quel AG début l’embryogénèse des yeux
Semaine 4
Que se passe-t-il au Jour 27 de l’embryogénèse?
By day 27,
* The optic vesicle starts to form in the neural ectoderm
* The lens placode forms in the surface, ectoderm
* The primary vitreous then extends to the future posterior lens has the hyaloid artery
Que se passe-t-il au Jour 29 de l’embryogénèse?
- The neural ectoderm invaginates to form the bilayer optic cup
- The surface ectoderm invaginates to form the lens vesicle
Que se passe-t-il au Jour 37 de l’embryogénèse?
By day 37,
The optic cup becomes more defined.
* The inner layer forms the neural retina
* The outer layer forms the retinal pigment epithelium.
The surface ectoderm has fully invaginated to form the lens and is separated from the future corneal epithelium.
* The posterior lens cells grow forward (as the primary lens fibers) which will form the embryo nucleus.
Next, the neural crest cells form additional corneal layers in two waves.
* The first wave for the future corneal endothelium.
* The second wave forms the future corneal stroma.
Que se passe-t-il au Jour 44 (sem 7) de l’embryogénèse?
By day 44, the conjunctival fornix in the eyelids start to form.
Que se passe-t-il au Jour 55 (sem 8) de l’embryogénèse?
Over the next 11 days (Jour 55, sem 8),
* The eyelids then come together and fuse, maintaining a conjunctival sac.
Que se passe-t-il 4e mois de l’embryogénèse?
By the fourth month,
- Folds of the ciliary processes appear.
- The iris sphincter develops.
- The hyaloid system starts to regress
- The Schlemm canal appears.
Que se passe-t-il 5e mois de l’embryogénèse?
At month five,
* The eyelid starts separate
* The eye has really taken shape.
* You can see the layers of the cornea, the anterior chamber, the lens, the sclera, the choroid, and the extra ocular muscles.
Tissu embryonaire du cristalllin
Surface ectoderm
Tissu embryonaire de l’épithéliun cornéen
**Surface ectoderm
**
* Lens formation begins with proliferation of surface ectoderm cells to form a lens plate, followed by inward invagination of the plate to form a lens pit.
* As the pit deepens, it closes anteriorly and detaches to form the lens vesicle,
* The remaining cells at the surface form the corneal epithelium.
Tissu embryonaire de l’endothélium et du stroma cornéen
Neural crest cells form the corneal stroma and endothelium, along with other anterior segment structures
Comment évolue/se développe le cristallin une fois la lens vesicle formée (post invagination de l’ectoderme de surface)
- The lens vesicle is a single- layer structure composed of cuboidal cells surrounding a large lumen, and it sits within the optic cup.
- The anterior cells remain cuboidal and single layered throughout life
- The rest of the lens epithelium cells become elongated, and their proliferation fills the optic vesicle.
- These posterior cells form the primary lens fibers that eventually form the embryonal nucleus.
- The remaining outer cells create a true basement membrane known as the lens capsule
Composition de la capsule du cristallin
- Type IV collagen
- Glycosaminoglycans
Tissu embryonaire de la neural retina et du RPE
Neuroectoderm
Although the physical space between these layers eventually closes, it remains a potential space; retinal detachments occur when fluid accumulates, due to various etiologies, within this space.
Première couche différentiée a/n de la rétine
Ganglion cells appear to be the first to differentiate; early in the second trimester, they proliferate rapidly
Origine de l’artère centrale rétinienne
Hyaloid artery
Pattern développement de la rétine et de la vascularisation de la rétine
Central puis extending peripherally
Conséquence d’un failure of fissure closures
Failure of fissure closure leads to a coloboma.
* Anterior colobomas are the most common (they cause iris and occasionally anterior scleral defects);
* Central colobomas are the least common;
* Posterior colobomas occur with a frequency somewhere in between (they give rise to optic nerve head, retinal, and choroidal defects).
Location of fissure closure
The location of fissure closure correlates with the inferonasal quadrant, which is where colobomas are clinically found.
The ONLY pigmented tissue in the body that is NOT derived from neural crest cells
RPE
(provient du neural ectoderm)
Structure précédant le NO
The optic nerve develops from the optic stalk, the narrow stalk that connects the optic vesicle with the forebrain.
Tissu embryonaire du NO
Neuroectoderm
Tissus embryonaires du vitré
The vitreous is probably formed from both mesodermal and ectodermal components:
* Neural crest cells of the inner optic cup probably contribute the connective fibers of the vitreous.
* The hyaloid vasculature develops from mesodermally derived cells
Tissu embryonaire de la vascularisation hyaloïde
The hyaloid vasculature develops from mesodermally derived cells.
Stades de développement du vitré
- The mesoderm gives rise to the hyaloid artery, which is contrained within the primary vitreous. (This vascular system supplies the tuinca vasculosa lentis).
- The secondary vitreous form from hyalocytes as the primary vitreous regresses.
- The zonular fibers develop from the tertiary vitreous.
Tissu embryonaire des eyelids
Surface ectoderm
Structures de l’uvée
- Corps ciliaire
- Iris
- Choroïde
Tissus embryonaires de l’uvée
Combination of mesoderm and neural crest cells
Caractéristiques des 2 couches épithéliales des processus ciliaires (inner versus outer layer, pigmentation)
- An inner pigmented layer
- An outer nonpigmented layer
The outer nonpigmented layer of the ciliary body is continuous with the retina posteriorly and the nonpigmented posterior epithelium of the iris anteriorly.
Tissus embryonaires de la choroïde
Combination of mesoderm and neural crest cells
Tissus embryonaires de la sclère
Combination of mesoderm and neural crest cells
Tissus embryonaires des EOMs
Combination of mesoderm and neural crest cells
Exemples de congenital cranial dysinnervation disorders involving the EOMs
- Duane retraction syndrome
- Marcus Gunn jaw- winking syndrome
- Möbius syndrome
- Congenital fibrosis of the extraocular muscles
Genetic studies have identified mutations in genes for neuron biology and axon guidance (ex. KIF21A, PHOX2A, TUBB3) that cause these EOM syndromes.
À quel âge début le lacrimal gland (reflex) tear production?
- Lacrimal gland (reflex) tear production does not begin until 20 or more days after birth.
- Therefore, newborn infants cry without tears.
Tissus embryonaires de l’orbite
Orbital development involves key contributions from ectodermal, mesodermal, and neural crest– derived elements.
Conséquences mutation/anomalie PAX6
- Ectopic eyes
- Aniridia
- Peters anomaly
- Coloboma
- Microphthalmia
Conséquence mutation/anomalie PAX2
Renal coloboma syndrome
Conséquence mutation/anomalie RAX
Microphthalmia
Conséquences mutation/anomalie PITX2
- Peters anomaly
- Axenfeld-Rieger syndrome
Conséquence de defects in Wnt signaling
Defects in Wnt signaling cause** familial exudative vitreoretinopathy** (incomplete vascularization of the peripheral retina), leading to vitreous bleeding, tractional retinal detachments, and severe visual impairment.
