Development of the Eye and the Ear Flashcards
Development of the eye begins with the formation of the optic vesicles which develop from the diencephalon. The growth of the optic vesicles extends outwardly towards the ____(a)____, eventually inducing it to thicken and form the ____(b)____. As the optic vesicles extend outwards towards the ____(a)____, the proximal portion of the vesicle constricts to form the ____(c)____ [also list its derivatives]. The distal portion of the optic vesicle is counter-induced by the ____(b)____ to invaginate and form the ____(d)____ [also list its derivatives].
The ____(b)____ eventually detaches to form the ____(e)____.
(a) surface ectoderm
(b) lens placode
(c) optic stalk; gives rise to the future optic nerve
(d) optic cup; gives rise to the retina, iris and ciliary body
(e) lens vesicle
[Diagram]
The optic cup has inner and outer layers [(a) what do they form?]. The cavity separating them is termed the ____(b)____ space [also state its fate]. The stem of the optic cup is termed the ____(c)____.
Invagination of the optic cup inferiorly leads to the formation of a groove termed the ____(d)____ which is invaded by an artery known as the ____(e)____ artery [state the structure it supplies]. This artery is the precursor of the central artery of the retina.
(a) outer layer: pigment retina, inner layer: neural retina, both also contribute to the formation of the iris
(b) intra-retinal; it eventually obliterates
(c) optic stalk
(d) choroid fissure [Diagram]
(e) hyaloid; it supplies the developing lens
Give reasons why the optic nerve is not considered a true peripheral nerve.
(a) it is derived from the diencephalon and hence is considered a tract of the diencephalon
(b) it is myelinated by oligodendrocytes [and not Schwann cells as with other peripheral nerves]
(c) it cannot regenerate when damaged, unlike other peripheral nerves
(d) the optic nerve is surrounded my meninges [pia, arachnoid and dura], unlike other peripheral nerves
Name the structures that give rise to the iris.
inner and outer layers of the optic cup rim
[Diagram]
lens placode ⇒ lens pit ⇒ lens vesicle
Outline the development of the lens after formation of the lens vesicle. Also breifly discuss nutrition of the lens.
✔ The lens vesicle comprises anterior and posterior walls with a cavity in between them.
✔ The cells that form the walls of the lens are initially cuboidal.
✔ However, during lens development, the cells of the posterior wall elongate, forming the lens fibres. The anterior cells remain cuboidal and give rise to the lens epithelium (subcapsular epithelium).
✔ During the development of the lens, it is supplied by the hyaloid artery which eventually regresses and the lens is thereafter nourished by the aqueous humor.
Outline the development of the sclera and the choroid.
The mesoderm around the optic cup differentiates into an outer fibrous layer, which forms the sclera, and an inner vascular layer which forms the choroid.
Anteriorly, the choroid is continuous with the ____(a)____; posteriorly, it is continuous with the ____(b)____ around the optic nerve.
Anteriorly, the sclera is continuous with the ____(c)____; posteriorly, it is continuous with the ____(d)____ around the optic nerve.
(a) ciliary body
(b) arachnoid mater
(c) cornea
(d) dura mater
Outline the embryonic origins of the cornea.
(a) The corneal epithelium is a derivative of the surface ectoderm.
(b) The corneal stroma, endothelium are derived from successive waves of invading neural crest cells.
Identify the congenital anomaly and state its embrological basis: [Click here].
coloboma iridis: caused by failure of closure of the choroid fissure
Identify the congenital anomaly and state its embrological basis: [Click here].
persistent iridopupillary membrane: failure of complete degeneration of the iridopupillary membrane, hence formation of web-like structures in front of the pupil
Identify the congenital anomaly and state its embrological basis: [Click here].
congenital cataract: opacity of the lens at birth. It is commonly associated with rubella virus infection, toxoplasmosis, Down’s syndrome, galactosemia etc.
Identify the congenital anomaly and state its embrological basis: [Click here].
microphthalmia: underdevelopment of the eye; may be associated with intrauterine infections e.g. rubella, herpes simplex
Identify the congenital anomaly and state its embrological basis: [Click here].
anophthalmia: absence of the eyeball caused by failure of development of the optic vesicle
Identify the congenital anomaly and state its embrological basis: [Click here].
congenital aniridia: absence of the iris due to arrest of development at the rim of the optic cup
