eye development Flashcards
At what stage does eye development begin?
17-19 days after fertilisation in early embryogenesis
how is eye development induced?
by interactions between the neuroectoderm and the ectoderm
when is a miniature eye formed?
by the end of the embryonic period at around 8 weeks
what are cells derived from the mesoderm layer responsible for?
-sclera
-bony orbit
-blood vessels
-ciliary muscle
-connective tissue
what are the 3 parts of the ectoderm and what do each of these parts contain?
- surface ectoderm:
-lens
-corneal epithelium
-conjunctival epithelium
-lacrimal glands
-tarsal glands
-epithelium of eyelids and cilia - neural ectoderm
-retinal pigment epithelium
-neural retina
-optic nerve fibres
-neuroglia
-epithelium of ciliary body
-epithelium of the iris - neural crest
-corneal stroma
-corneal endothelium
-uveal melanocytes
-uveal connective tissue
where do cells destined to form the eyes reside?
the field in the anterior neural plate
give an eye defect as a result of early developmental disruption
cyclopia which is where the eye fields fail to separate during week 3 of development leading to the formation of a single eye
what happens in eye development when the embryo is 4 weeks old?
formation of the optic vesicle, optic stalk and lens placode, early development of brain and spinal cord also begin
when and what is the infolding of the neural plate?
at day 24 where the edges of the cranial neural folds fold inwards and fuse at the same time, forcing the optic groove into close contact with the surface ectoderm
what are the first definitive structures of the developing eye to form and when do they form
the optic vesicles which grow outwards from the forebrain, they form between day 25-28
what happens with the eye at week 5?
-invagination of the optic vesicle to form the optic cup
-invagination of the lens placode to form the lens vesicle
-formation of the choroidal fissure
-hyaloid vessels form network to nourish the lens
how do hyaloid vessels grow through the choroidal fissure?
- primitive blood vessels enter the closing fissure along the underside of the optic stalk growing forward to the rim of the cup and lens
- the hyaloid vessels form a capillary network surrounding the developing lens
hyaloid vessels are not present in adults
what happens to the eye development at week 6?
-closure of the lens vesicle as it pinches off of the surface ectoderm to form the hollow primitive lens
-closure of the choroidal fissure completes formation of the optic cup
-retina starts to differentiate
why does the lens pinch off of a patch of surface ectoderm at the end of it’s formation?
due to contraction of the sub membranous actin cytoskeleton linked to zonulae adherents
what is coloboma? what is it caused by? what does it lead to?
a gap in part of structures of the eye due to incomplete closure of the choroidal fissure which leads to failure of induction of multiple structures such as iris, ciliary body, choroid, retina and lens
How is the retina from the optic cup formed?
- as the choroidal fissure closes, the two layers of the retina start to differentiate
- the pigmented layer remains one cell thick while the neural portion thickens
- the neural part of the retina differentiates into numerous distinct cell layers
what happens in eye development at week 7?
-lens develops many primary fibres
-formation of cornea and anterior chamber
-formation of iridopupillary membrane
-the neural retina starts differentiating into different cell types
what are the steps in the further development of the lens?
- hyaloid vasculature surrounds the back of the developing lens to support lens growth
- lens fibres begin elongation
how does the cornea further develop?
- cornea starts to differentiate
- outer epithelial layer gets derived from surface ectoderm
- inner layers get derived from the neural crest
how do the anterior chamber and iridopupillary membrane form?
-anterior chamber develops between the lens and the iridopupilliary membrane and cornea
-iridopupilliary membrane is initially attached to the lens and influences lens presence as it develops
how does the retina develop?
- pigmented layer becomes relatively thinner while the neural portion thickens
- neural portion differentiates into several layers
what happens in eye development at week 8 and on?
-regression of iridopupillary membrane
-formation of the corneal epithelium and primary stroma
-development of iris and cilliary body
-development of secondary fibres
-formation of eyelids
what does the cornea consist of at week 8?
an outer epithelial layer derived from the surface ectoderm and inner layers derived from neural crest
how does the lens further develop in week 8?
- proliferation of the epithelial cells at the equator
- anterior cells at pole of lens elongate and surround primary fibres forming a complete ring
- formation of secondary fibres
give a development anomaly of the lens and explain what are its 2 causes
congenital cataract
-misalignment of the primary lens fibres due to failure of proper induction from the optic cup/retina leads to cataract in the embryonic nucleus
-viral infection: rubella can persist in the lens for up to 3 years and disturbs formation of primary lens fibres so can only tale affect during weeks 4-7
name an anomaly of the vitreous and it’s cause
persistent hyperplastic primary vitreous
caused by remnants of the hyaloid vessels that persist in the vitreous
when do eyelids form, fuse and reopen?
form in week 8, fuse at the start if the 2nd trimester and reopen at the start of the 3rd trimester
what is anophthalmos?
complete absence of the eye where the opticle vesicle forms but the eye fails to develops
what is microphthalmos? why? what could it be caused by?
a small eye possibly due to failure of optic cup expansion and correct development of retina and vitreous
could be caused by chromosome abnormalities like trisomy 13, infections during pregnancy like rubella or foetal alcohol syndrome