Origin OF THE EYEBALL
INTRODUCTION:
The eyeball is formed from both ectoderm and mesenchyme. The ectoderm that
is derived from the neural lube gives rise to the retina. The nerve fibers of the optic nerve,
and the smooth muscle of the iris. The surface ectoderm on the side of the head from
corneal and conjunctival epithelium ,the lens and the lacrimal and tarsal gland. The
mesenchyme forms the corneal stroma, the sclera, the choroid, the iris, the ciliary body and
the part of the vitreous body, and the cell lining of the interior chamber. The endothelium of
the cornea is believed to be of neural crest origin.
THE EYEBALL:
The rudimentary eyeball develops as an ectodermal diverticulum from the lateral
aspect of the forebrain. The diverticulum grows out laterally towards the side of the head and
the end becomes slightly dilated to form the optic vesical, while the proximal portion
becomes constricted to form the optic stalk. At the same time, a small area of the surface
ectoderm overlaying the optic vesical thickened to form the lens placode. The lens placode
invaginated and sinks below the surface ectoderm to become the lens vesicle. Meanwhile ,
the optic vesicle becomes invaginated to form the double layered optic cup. The inferior
edges of the optic cup are deficient,and this notch is continuous with the groove on the
inferior aspect of the optic stalk called the optic and choroidal fissure. Vascular
mesenchyme now grows into the optic fissure and takes with it hyaloid arteries. Later, this
fissure became narrowed by growth of its margins around the artery, and by the seventh
week of embryonic development the fissure closes, forming a narrow tube, the optic canal
inside the optic stalk. Failure of the fissure to close completely results in coloboma formation,
which may include the pupil, ciliary body, and choroid or optic nerve. By the fifth week, the
lens vesicle loses the contact with the surface ectoderm and lies within the mouth of the
optic cup, the edges of which form the future pupil.
THE RETINA:
The retina develops from the optic cup. Retina may divide into the two developmental layers,
the pigment layer and the neural layer.
The pigmented layer is formed by the outer thinner layer of the optic cup. It is a
single layer of the cells that become columnar in shape and develop pigment granules
(melanosomes) within their cytoplasm.
The neural layer is formed from the inner layer of the optic cup. However, in the
region of the cup that overlaps the lens the inner is not differentiated into nervous tissue.
This anterior one- fifth of the inner layer of columnar cells, which together with the pigmented
epithelium of the outer layer, extend forward onto the posterior surface of the developing
ciliary body and iris.
The posterior four-fifths of the inner layer of the optic cup undergoes cellular
proliferation, forming an outer nuclear zone and an inner marginal zone, devoid of nuclei.
Later , the cells of the nuclear zone invade the marginal zone so that the neural part of the
retina is made up of an outer neuroblast layer. The inner neuroblastic layer forms the
ganglion cells, the amacrine cells, and the bodies of the sustentacular fibers of muller. The
outer neuroblastic layer gives rise to the horizontal and rod and cone bipolar nerve cells and
the rod and cone cells. By the eight month of fetal life all the layers of the retina can be
INTRODUCTION:
The eyeball is formed from both ectoderm and mesenchyme. The ectoderm that
is derived from the neural lube gives rise to the retina. The nerve fibers of the optic nerve,
and the smooth muscle of the iris. The surface ectoderm on the side of the head from
corneal and conjunctival epithelium ,the lens and the lacrimal and tarsal gland. The
mesenchyme forms the corneal stroma, the sclera, the choroid, the iris, the ciliary body and
the part of the vitreous body, and the cell lining of the interior chamber. The endothelium of
the cornea is believed to be of neural crest origin.
THE EYEBALL:
The rudimentary eyeball develops as an ectodermal diverticulum from the lateral
aspect of the forebrain. The diverticulum grows out laterally towards the side of the head and
the end becomes slightly dilated to form the optic vesical, while the proximal portion
becomes constricted to form the optic stalk. At the same time, a small area of the surface
ectoderm overlaying the optic vesical thickened to form the lens placode. The lens placode
invaginated and sinks below the surface ectoderm to become the lens vesicle. Meanwhile ,
the optic vesicle becomes invaginated to form the double layered optic cup. The inferior
edges of the optic cup are deficient,and this notch is continuous with the groove on the
inferior aspect of the optic stalk called the optic and choroidal fissure. Vascular
mesenchyme now grows into the optic fissure and takes with it hyaloid arteries. Later, this
fissure became narrowed by growth of its margins around the artery, and by the seventh
week of embryonic development the fissure closes, forming a narrow tube, the optic canal
inside the optic stalk. Failure of the fissure to close completely results in coloboma formation,
which may include the pupil, ciliary body, and choroid or optic nerve. By the fifth week, the
lens vesicle loses the contact with the surface ectoderm and lies within the mouth of the
optic cup, the edges of which form the future pupil.
THE RETINA:
The retina develops from the optic cup. Retina may divide into the two developmental layers,
the pigment layer and the neural layer.
The pigmented layer is formed by the outer thinner layer of the optic cup. It is a
single layer of the cells that become columnar in shape and develop pigment granules
(melanosomes) within their cytoplasm.
The neural layer is formed from the inner layer of the optic cup. However, in the
region of the cup that overlaps the lens the inner is not differentiated into nervous tissue.
This anterior one- fifth of the inner layer of columnar cells, which together with the pigmented
epithelium of the outer layer, extend forward onto the posterior surface of the developing
ciliary body and iris.
The posterior four-fifths of the inner layer of the optic cup undergoes cellular
proliferation, forming an outer nuclear zone and an inner marginal zone, devoid of nuclei.
Later , the cells of the nuclear zone invade the marginal zone so that the neural part of the
retina is made up of an outer neuroblast layer. The inner neuroblastic layer forms the
ganglion cells, the amacrine cells, and the bodies of the sustentacular fibers of muller. The
outer neuroblastic layer gives rise to the horizontal and rod and cone bipolar nerve cells and
the rod and cone cells. By the eight month of fetal life all the layers of the retina can be
