Ocular embryology

Ocular Embryology
Presentation By:
Kartik Kumar Gupta
B. Optometry-2nd Year
BV(DU)MC School of Optometry

Presentation Layout
1. Introduction on general embryology
2. Ocular embryology
3. Milestone in the development in ocular structure
4. Congenital anomalies of the eye and its adnexa
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Spermatogenesis, Oogenesis and Zygote formation
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Female Reproductive System
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Development Of Zygote
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Embryological Term
1. Oocyte (L. Ovum = egg): Female germ or sex cells
produced by ovaries.
2. Sperm (Gr. Sperma = seed): Male germ cells produced by
testes.
3. Zygote: Cell formed by union of a sperm and secondary
oocyte (ovum). The zygote is the earliest stage of embryo
(i.e., the beginning of the new human being).
4. Conceptus: Product of conception, i.e., embryo along with
its extraembryonic membranes.
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Embryological Term cont’d…
5. Cleavage: Series of mitotic divisions of the zygote to form
early embryonic cells—the blastomeres.
6. Morula (L. Morus = mulberry): Solid ball of 12–32 cells
(blastomeres) formed 3–4 days after fertilization, just at
the time when embryo enters the uterus.
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7. Blastocyst (Gr. Blastos = bud, Kystis = bladder):
o It forms at late morula stage when fluid passes into
intercellular spaces between the inner and outer layers of
cells and forms a fluid-filled cavity.
o The blastocyst is divided into two parts: an outer layer called
trophoblasts and inner cell mass called embryoblast.
o The cavity of blastocyst (blastocele) separates the
trophoblast from the inner cell mass except for a small area
where they are in contact.
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8. Implantation: Attachment and subsequent embedding of
blastocyst into uterine endometrium, where it develops
during gestation. Implantation occurs between fifth and
seventh day after fertilization.
9. Gastrulation: Formation of three germ layers (ectoderm,
mesoderm, and endoderm) in the embryo. It is the most
characteristic event during the third week of gestation.
10.Neurulation (Gr. Neuron = nerve): Process by which neural
plate forms the neural tube.
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11.Embryo (Gr. Embryon): Developing human from
conception to eighth week in uterus. This period is called
embryonic period (or period of organogenesis). By the end
of this period primordia of all the major structures of the
body are formed.
12.Primordium (L. Primus = first + Ordior = to begin):
Beginning or first discernible indication of an organ or
structure.
13.Fetus (L. Unborn = offspring): Developing human from
ninth week to birth. During this period (fetal period),
differentiation and growth of the tissues and organs
formed during the embryonic period takes place.26-06-2020 18

14.Abortion (L. Aboriri = to miscarry): Expulsion of a
conceptus (embryo or fetus) before it is unable, i.e.,
capable of living outside the uterus.
15.Gestation (L. Gestatio = bearing, carrying in the womb):
The duration of embryo in the uterus from fertilization of
the ovum until delivery (the period of normal pregnancy).
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Embryologic Derivation of Ocular Structures
Surface ectoderm gives rise to:
Lens
Corneal epithelium
Conjunctival epithelium
Epithelium of eyelids and cilia, meibomian glands, and
glands of Zeis and Moll
Epithelium lining nasolacrimal system
Lacrimal gland and epithelial lining the lacrimal apparatus
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Embryologic Derivation of Ocular Structures cont’d…
Neural ectoderm gives rise to:
Retinal pigment epithelium
Neural retina
Optic nerve fibers
Neuroglia
Epithelium of ciliary body
Epithelium of iris
Iris sphincter and dilator muscles
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Embryologic Derivation Of Ocular Structures Cont’d…
Neural crest gives rise to:
Corneal stroma (which gives rise to Bowman’s layer)
Corneal endothelium (which gives rise to Descemet’s
membrane)
Most (or all) of sclera
Trabecular structures
Uveal pigment cells
Uveal connective tissue
Ciliary muscle
Meninges of optic nerve
Vascular pericytes
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Fig. Optic Fissure26-06-2020 28

Optic Cup and Lens Vesicle
Choroidal fissure develops on the inferior aspect of the optic cup and optic
stalk
Lens vesicle enters into the optic cup
Optic vesicle invaginate to form double layer optic cup
lens pits
Optic vesicle comes in contact with surface ectoderm; form lens placode
Proximal part connected to forebrain constricted to form optic stalk
Optic vesicle
Optic groove/sulcus
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Development Of Various Part Of
Eyeball
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Development Of Eyelid, Conjunctival Sac And
Lacrimal Gland Cont’d…
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Milestone In The Development
Of Ocular Structures
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Pre-embryonic Period (Fertilization To End Of 3rd Week)
Formation of the principle germinal layer
Formation of neural plate and neural groove
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Embryonic Period (Beginning Of 4th To End Of 8th Week)
22 Days:
Appearance of optic pits in the neural fold.
25 To 28 Days:
Invagination of primary optic vesicle
Beginning of lens placode formation
Condensation of mesoderm determining extraocular
muscles.
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5th Week Of Embryonic Period
Full development of primary optic vesicle
Earliest appearance of the primitive and marginal zones of
the presumptive retina.
Beginning of invagination of optic vesicle to form optic cup
Formation of the lens pit
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5th Week Of Embryonic Period Cont’d….
Ophthalmic artery emerges from the internal carotid
Development of embryonic fissure
Hyaloid artery emerges from the primitive dorsal
ophthalmic artery
Lens pits has developed into a closed vesicle in contact with
surface ectoderm.
Hyaloid artery enters the embryonic fissure and reaches up
to posterior pole of the lens vesicle.
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Lens vesicle become hollow sphere detached from ectoderm
Hyaloid artery takes part in the formation of the posterior
part of the tunica vasculosa lentis.
Beginning of the closure of embryonic cleft in its mid-
portion.
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Second stage of retinal differentiation with formation of
primitive inner nuclear layer.
Formation of lens fibers from posterior epithelial cells of
lens vesicle.
Almost complete closure of embryonic fissure except at
anterior and posterior extent.
Optic nerve fibers travelling proximally into optic nerve.26-06-2020 47

Beginning of development of secondary vitreous.
Choriocapillaris is completely formed.
Double layer of cells at the surface ectoderm forms the
corneal epithelium.
Orbital mesoderm begins to differentiate into extraocular
muscles.
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• Distal end of the embryonic fissure is completely closed.
• Differentiation of inner and outer neuroblastic layers of
retina affected by appearance of transient fibre layer of
Chievitz at posterior pole.
• Rudiments of lids have developed into definite folds and the
fibers of the orbicularis oculi muscle begin to surround the
eye.26-06-2020 49

Formation of anterior portion of tunica vasculosa lentis
Proximal remnant of embryonic fissure closed.
Beginning of nerve fibres crossing to form optic chiasma
Separation of corneal epithelium and endothelium by
acellular layer.
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Nuclei of primary lens fibres disappears.
Lids folds gradually covers the eyes.
Canaliculi are present.
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Optic chiasma is fully formed.
Penetration of acellular layer of cornea by mesoderm to
form corneal stroma.
Pupillary membrane is completely formed.
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• Beginning of the anterior chamber can be recognized.
• All the motor nerves of the eye have reached the extraocular
muscles.
9th Week
• Ciliary body is begins to appear.
• Secondary vitreous is fully evident.
• Y-suture are now apparent in the embryonic nucleus of the
lens.
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Zonule makes its appearance Bowman’s membrane is
forming.
Tenon’s capsule begins to form in the equatorial region.
Fibers of the orbicularis oculi are forming.
At the end of this period, optic tract have formed.
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Macula begins to differentiate.
Differentiation of the occipital cortex appears.
The hyaloid system is maximally developed.
Rectus muscles are well differentiated and levator separates
from superior rectus.
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4th Month
• Ciliary processes are fully formed.
• Secondary vitreous develops considerably.
• Lashes and gland of the lids appear and the plica is well formed.
• Tenon’s capsule is fully formed.
• Orbital walls are well developed.
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5th Month
Myelination in the geniculate body is evident.
All layers of the choroid are now visible and melanoblasts
appear in its external portion.
Iris is fully developed.
Extraocular muscles have differentiated their tendinous insertion
Dural sheath of the optic nerve can be distinguished.
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6th Month
Dilator pupillae begin to form.
Sphincter muscle of the pupil is fully differentiated.
Descemet’s membrane has appeared.
Anterior chamber angle is forming peripherally.
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7th Month
Rods are differentiated in the retina.
Fovea become obvious.
Bergmeister’s papilla begins to atrophy.
Lacrimal canaliculi have opened on the lid margins and the
tarsus is well formed in the upper lids.
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8th Months
All layer of the retina are extensively developed throughout.
Retinal vessels have reached the ora.
Fetal nucleus of the lens is complete.
Circulation of the anterior segment is complete.
Angle of anterior chamber is formed completely.
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9th Month
• Diameter of the globe increase to 16 to 17mm.
• Except macula, general development of the retina is now
complete.
• Retinal vessels reach the periphery.
• Infantile nucleus of the lens begins to appear.
• Pupillary membrane and hyaloid vessels have disappeared.
• Formation of the physiologic cup of the disc begins.
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At Term
Apart from the fovea, the retina is fully developed.
Myelination of optic nerve fibre has reached lamina
cribrosa.
Coiled remnants of the hyaloid artery have attached
anteriorly up to the posterior lens capsule and float freely in
Cloquet’s canal.
Lacrimal glands are still undeveloped and tears are not
secreted.
Nasolacrimal duct has reached the nasal cavity but is
frequently separated from the inferior meatus by a
membrane.26-06-2020 62

Postnatal period
Orbit
Angle between orbital axes is 180 degree, at birth 71 degree
and 68 degree in adult.
Volume of the orbit at birth is 10.3 ml, 22.3ml at 1 year and
reaching the adult volume of 30 ml by 6-8 years.
Bony interorbital distance is hypoteloric due to absence of
frontal and ethmoid air cells which gives the appearance of
pseudostarbismus.
Optic canal at birth is actually a foramen but later becomes
canal, and at 1 year its length is 4mm.
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Lids And Lacrimal Apparatus
Vertical Dimensions
• Infants: 8-8.5mm
• 1-10 year: 9mm
Horizontal Dimensions
• At Birth: 18mm
• 1-10 year: rapid increase to adult level of 30mm
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Lacrimal System
Excretory and secretory functions of the lacrimal apparatus
are operational in most normal infants at birth.
Basal and reflex tear secretion in more than 80% infants at
birth, psychic and emotion tearing occurs several months
after life.
Development of NLD is complete at birth.
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IOP
Low at birth 7.8±0.4 mm Hg and increases 1mmHg/year for
5 years to reach adult level.
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Uveal Tract And Pupil
Dilator pupillae is poorly developed and does not reach
adult proportions until about the 5th year.
Iris stromal pigments develops after birth; so in white races
this tissue is initially light blue in colour for sometimes.
Pupillary light reaction is normal at birth.
Pars plana zone at birth is underdeveloped and pars plicata
is within just behind limbus.
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Lens
• Lens capsule increase in thickness especially anteriorly.
Hyaloid remnants at the posterior capsule gradually atrophy
through childhood.
• Nucleus: Although, the infantile nucleus is present at birth it
continues to grow by accumulation of new fibers up to
puberty.
• Cortex: the accretion of new fibers forms cortex, which
continues through out life.
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Macula
• Development of retina lags behind rest of the retina and thus
considerable changes occur after the birth.
• Differentiation of all layers proceeds during the first 4
months, at the end of which period the characteristic foveal
reflex is present on ophthalmoscopy.
• Macula is barely functional at birth. Histologically and
functionally mature by 4 years.
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Macula cont’d…
Histologic Maturity:
1. Foveolar diameter (rod-free zone)
Birth : 1100 micrometre
15 – 45 months : 700 – 750
2. Foveal cone maturation is completed by 15 months.
3. Foveal cone density
Birth: 18 cones/100
45 m: 31 cones
Adult: 42
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Macula Cont’d…
Functional Maturity:
Visual fixation is present at birth and is well developed by 2
months.
Visual following is well developed by 3 months.
Differentiation of fovea is completed by 4 months and
characteristic foveal reflex is present on ophthalmoscopy.
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Optic Disc
Colour:
1. At birth, the disc is relatively and uniformly pale when
compared to the pink colour of the older disc.
2. However, this changes to the normal adult pink colour by about
6 months to 1 year of age.
Physiological Cupping:
1. Not seen in premature infants or underdeveloped full term
infants, such that the optic disc may appear grey at birth
resembling optic nerve atrophy.
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Peripheral Fundus
Still lacks the pigmentation of the adult.
The choroidal vessels are distinctly visible.
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Optic Nerve And Upper Visual Pathway
Myelination proceeds from occipital cortex downward and is
not complete until the end of the fourth month.
 Myelination of the optic nerve begins during foetal life at
the lateral geniculate body and reaches the optic disc around
the time of birth.
Normally, the myelin does not extend anterior to the
cribriform plate.
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Refractive Status
• Term infant : +0.62 – 2.24D
• Increases up to 7 years of age
• Then decreases and stabilizes by 14-15 years
• Myopic shift:
- In hypermetropes - 0.12 D / year
- In myopes - 0.55 D / year
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Visual Acuity
• Postnatal maturation of visual pathway plays an important
role in development of vision.
• The 1st year of life remains the dynamic and plastic period for
visual development.
• Any pathology during this period will impair its development.
• The visual system remains malleable at least during first
decade of life, and attention to this plasticity is considered
for the prevention and treatment of amblyopia.
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Maturation Of Vision
• Optokinetic nystagmus is well developed at birth.
• Accommodation is well developed by 4 months.
• Ocular alignment becomes stable by 1 month.
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Levels Of Visual Acuity
Visual acuity 1 months 2 months 6 months Age at which 6/6 is
achieved
Optokinetic
nystagmus
6/120 6/60 6/30 20-30 months
Preferential
looking
6/120 6/60 6/30 24-36 months
VEP 6/120 6/60 6/6-6/12 6-12 months
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Stereopsis
• Development of stereopsis roughly parallels the
development of visual acuity. It can be demonstrated at 3 – 6
months of age and rapidly improves thereafter.
• Stereopsis ( titmus ) at adult level is achieved by 7 yrs.
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Visual Fields
Using suitable kinetic perimetry, the monocular visual fields
in new-borns extend 28 degrees to left and right of the
vertical meridian, and 11 degrees above and 16 degrees
below the horizontal meridian.
Rapid expansion in dimension of the visual fields follows,
and at 1 year of age the superior visual field is comparable to
that of adults.
By 10 years of age, adult visual field size is attained.
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Eye Movements
Initially, eye movements are irregular and not conjugate.
But by 5 – 6 weeks, the eyes can follow a light over a
considerable range.
Pursuit of small objects occurs at about 3 months and
transition from reflex to conscious fixation becomes
apparent; but conjugate fixation is not accurate until about 6
months, until convergence is established.
Corrective fusion reflexes are fully functional towards the
end of 1st year.
26-06-2020 81

Visual Milestones
Age Visual Milestones
• 29 weeks Gestation Pupillary reaction to light
• 30 weeks G to Birth Dislike bright light
- turns to subdued light
• Birth - 1 week Fixation present
- Follow horizontally moving
targets –OKN and vestibular
eye movements well
developed.
- Visual acuity on Acuity cards
(6/120)
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Visual Milestones continued…
• 4 weeks – 8 weeks Fixation well developed
- Follows vertically moving
objects
- Fusion develops
- Watches mother’s face intently
for prolonged duration
- Watches toys held in front of
face
- Doll’s head eye movements
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• 3 months Watches movements of own hands
- Reaches out to interesting
objects
- Prefers photographs, mirror
faces to patterns
• 4 months Foveal differentiation completed
Accommodation developed
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• 5 months Blink response to visual threat
- Grasps object and explores with
finger
• 6 months - VEP acuity adult level (6/6)
- Stereopsis on PLT well
developed
- Fusional convergence well
developed
26-06-2020 85

Visual Milestones continued..
• 9 months Visual differentiation of objects,
picks up small objects
• 18 months Visual acuity (Acuity cards : (6/6)
• 3 years Vision 6/9 - 6/6 On Tumbling E /
HOTV (Recognition)
- Contrast Sensitivity adult level
• 5 – 7 years Stereopsis well developed
• 10 years End of critical period for
monocular deprivation (synapse
formation completed)26-06-2020 86

Congenital Anomalies
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Persistent Pupillary Membrane
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Coloboma Of Iris
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Congenital Aniridia
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Coloboma Of Eyelid
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Congenital Ptosis
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Bergmeister’s Papilla
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Retinopathy Of Prematurity
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Persistent Hyperplastic Primary Vitreous
26-06-2020 101

Ocular embryology

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