Transcript Cont… - MBBS Students Club | Spreading medical knowledge

DEVELOPMENT OF EYE
DEVELOPMENT OF EYE
Eyes are derived from four sources
• Neuroectoderm of fore brain
retina, posterior layers of iris, optic nerve
• Surface ectoderm of head
Lens& corneal epithelium
• Mesoderm between above layers
Fibrous & vascular coats
• Neural crest cells
choroid, sclera & corneal endothelium
OPTIC PRIMORDIA
The developing eye appears in the 22-day
embryo as a pair of shallow grooves on
each side of the forebrain.
DEVELOPMENT OF OPTIC CUP
& LENS VESICLE
• With closure of neural tube these grooves will form
outpocketings of the forebrain, optic vesicles
• On contact with surface ectoderm, these vesicles induce
changes for lens formation, shortly there after the
vesicles invaginate and form the double walled optic cup
Cont…
• The inner and outer
layers of optic cup are
separated by
intraretinal space,
soon the lumen
disappears and the
layers fuse
• Rim of the cup in folds
around the lens vesicle
Cont…
• Invagination is not restricted to the central part of
optic cup but also involves part of inferior
surface that forms the retinal / choroid fissure
Cont…
• Vascular mesenchyme give rise to hyaloid
vessels which supplies the inner layer of optic
cup, lens vesicle & mesenchyme in optic cup
Cont…
• As the edges of retinal fissure fuse these
vessels are enclosed with in primordial optic
nerve
• Distal parts of these vessels degenerate while
proximal parts persist as central artery & vein of
retina
Cont…
On contact of optic vesicle
with surface ectoderm,
the cells of surface
ectoderm elongates and
form the:
• Lens placodes
• Lens pit
• Lens vesicle
DEVELOPMENT OF RETINA
Retina develops from the walls of optic cup
• Outer layer
Pigment epithelium of retina
• Inner/Neural layer
Posterior 4/5th pars optica retinae (NeuroEp)
Rods &
Cones
Mantle
zone
Intraretinal space; disappears when two layers fuse
• On the surface are the axons of
ganglion cells that grow in optic
stalk to form optic nerve fiber
layer
• Neural retina is inverted
• Light impulses pass through
most layers of retina before they
reach photoreceptors
pars ceca retinae
The anterior 1/5th of the inner layer of retina (pars ceca
retinae ) divides into:
• Pars iridica retinae ---- inner layer of iris
• Pars ciliaris retinae ---- ciliary body
The region b/w the optic cup and the overlying surface
epithelium is filled with loose mesenchyme.
CILIARY BODY
• Is the part of anterior 1/5th of the inner layer
• Medial surface projects towards lens forming folds --- ciliary
processes
• The pigmented outer portion of ciliary epithelium is derived from
outer layer of optic cup & is continuous with retinal pigment Ep.
• The nonpigmented portion of ciliary Ep. represent the anterior
prolongation of neural retina and consist of single layer of epithelium
• The ciliary muscle develops from the mesenchyme of optic cup---smooth muscle for focusing the lens
DEVELOPMENT OF IRIS
Develops from rim of optic cup that grows inwards & partly
covers the lens
Iris is formed by:
• The pigment containing external layer continuous with the
pigment epithelium of ciliary body & neural retina
• The unpigmented internal layer of the optic cup
C.T frame work is derived from neural crest cells that migrate
into iris
The dilator pupillae & sphincter pupillae muscles develop
in the surrounding mesenchyme and are derived from the
underlying ectoderm of the optic cup
DEVELOPMENT OF LENS
LENS VESICLE:
Derivative of surface ectoderm
Anterior wall :
Cuboidal Ep (sub capsular lens Ep.)
Posterior wall :
Tall Columnar Ep--- nuclei dissolute
cells elongate anteriorly & form
primary lens fibers which gradually
obliterate the lumen of lens vesicle
The rim of lens, midway between
anterior & posterior poles of lens
Cells are cuboidal first, elongate, lose
nuclei & form secondary lens fibers which
re continued to form during adult hood
Initially by distal part of hyaloid artery
which degenerates; later it depends upon
aqueous humor & Vitreous humor
Equatorial zone :
Nutrition of lens:
Tunica vasculosa lentis: capsule of lens
Anterior part forms pupillary membrane
Both degenerate when hyaloid A. degenerates
However the lens capsule produced by anterior lens
Ep. & lens fibers persist
DEVELOPMENT OF VITEROUS BODY
• Forms within the cavity of optic cup
• Mesenchyme not only surrounds the eye primodium but
also invades the inside of optic cup by way of choroidal
fissure
• Here it forms hyaloid vessels which supplies posterior
surface of lens& forms a vascular layer on inner surface
of retina
• Forms delicate network of fibers
between retina & lens
• Interstitial space fills with delicate
gelatinous substance forming
vitreous body
• Hyaloid vessels disappear leaving
hyaloid canal only
DEVELOPMENT OF AQUEOUS
CHAMBERS
• ANTERIOR CHAMBER develops from clefts that appear
in the mesenchyme between developing lens & cornea
• POSTERIOR CHAMBER develops from the space that
forms in mesenchyme posterior to developing iris &
anterior to developing lens
• When pupillary membrane disappears & pupil forms the
anterior & posterior chambers of the eye are able to
communicate with each other. The clear aqueous humor
circulates from posterior to anterior chamber and
provides nutrients for cornea and lens. From anterior
chamber the fluid passes through the scleral venous
sinus (canal of Schlemm) at the iridocorneal angle where
it is resorbed into blood stream. This drains the anterior
chamber into venous system
DEVELOPMENT OF CHOIRD, SCLERA &
CORNEA
• Under the inductive influence of retinal pigment
epithelium the mesenchyme surrounding the optic
cup differentiates into an inner vascular pigmented
layer, the choroid & outer fibrous layer, the sclera
• Choroid becomes modified to form cores of ciliary
processes containing delicate capillaries & fine C.T
• Sclera is continuous with corneal stroma
• Lens vesicle induces the formation of cornea
by transforming surface ectoderm into transparent,
multi layered,a vascular cornea
CORNEA is formed from three sources
1. External corneal Ep.--- surface ectoderm
2. Mesenchyme (stroma) --- continuous with
sclera
3. Internal corneal endothelium--- neural crest
cells
COLOBOMA & PERSISTENCE
OF PUPILLARY
CYCLOPIA & ANOPHTHALMIA