2. Embryology of Human Eye
By: Sumayya Naseem
Optometrist
Research Officer, School Eye Health Programme, Pakistan.
CHEF International

3. Embryo & Embryogenesis…. A short Introduction
In humans, an embryo is the name given to a form until about eight weeks
after fertilization and from then it is instead called a fetus.
The development of the embryo is called embryogenesis.
In organisms that reproduce sexually, once a sperm fertilizes an egg cell, the
result is a cell called the zygote that has half of the DNA of each of two parents.
In plants, animals, the zygote will begin to divide by mitosis to produce a
multicellular organism. The result of this process is an embryo.

4. Optic Cup and Lens Vesicle
 The developing eye appears in the 22-day embryo as a pair of shallow
grooves on the sides of the forebrain.
 These grooves form outpocketings of the forebrain, the optic vesicles (4 th
week).
 The optic vesicle begins to invaginate and forms the double-walled optic
cup (formation of Optic Cup).
(Transverse section through the forebrain of embryo)

5. Optic cup —invagination of distal
optic vesicle to form double walled
“cup
Lens pit—invaginates to form
lens vesicle
The cells of the surface ectoderm
begin to elongate and form the lens
placode.
This placode subsequently
invaginates and develops into the
lens vesicle.

6. The inner and outer layers of this cup are initially separated by a lumen,
the intraretinal space,
This lumen disappears, and the two layers appose each other.

7. Optic (choroid) fissure —sulcus
on ventral aspect optic cup/stalk
Invagination is not restricted to the
central portion of the cup but also
involves a part of the inferior surface
that forms the choroid fissure.
Formation of this fissure allows the
hyaloid artery to reach the inner
chamber of the eye.

8. Iris Muscles , Pupil
 The sphincter and dilator pupillae muscles form in this tissue.
 These muscles develop from the underlying ectoderm of the optic
cup.
 In the adult, the iris is formed by the pigment-containing external
layer, the unpigmented internal layer of the optic cup, and a layer of
richly vascularized connective tissue that contains the pupillary
muscles.

9. Choroid & Sclera
 At the end of the fifth week,
tissues soon differentiates into an inner layer comparable with the
pia mater of the brain and an outer layer comparable with the
dura mater.
 The inner layer later forms a highly vascularized pigmented layer
known as the choroid.
 The outer layer develops into the sclera and is continuous with the
dura mater around the optic nerve.

10. Optic Nerve
 The optic stalk is thus transformed into the optic nerve.
 Its center contains a portion of central artery of the retina.
 On the outside, a continuation of the choroid and sclera, the pia
arachnoid and dura layer of the nerve, respectively, surround the
optic nerve.

11. B. Seventh week (15 mm). C. Ninth week
A. Sixth week (9
mm).
Transformation of the optic stalk into the optic nerve.
(Note the central artery of the retina)

12. VISUAL REFLEXES
 Pupillary Light Reflexes: 30wks gestation
 Constriction (parasympathetic)
 Dilatation (sympathetic)
 Accommodation (4 months = well developed)
Accommodation.mp4 Accommodation and natural lens.mp4

13. CLINICAL CORRELATES
Eye Abnormalities
Coloboma may occur if the choroid fissure fails to close. (Normally this
fissure closes during the seventh week of development).
 Coloboma iridis.
 Coloboma is a common eye abnormality frequently associated
with other eye defects.
 Colobomas (clefts) of the eyelids may also occur.

14. CLINICAL CORRELATES
Eye Abnormalities
The iridopupillary membrane in front of the lens disappears
completely, providing communication between the anterior and
posterior eye chambers.
The iridopupillary membrane may persist instead of being
resorbed during formation of the anterior chamber.

15. CLINICAL CORRELATES
Eye Abnormalities
 In congenital cataracts the lens becomes opaque during intrauterine
life. Although this anomaly is usually genetically determined, many
children of mothers who have had German measles (rubella)
between the fourth and seventh weeks of pregnancy have cataracts.
 (If the mother is infected after the seventh week of pregnancy, the
lens escapes damage, but the child may be deaf as a result of
abnormalities of the cochlea)

16. CLINICAL CORRELATES
Eye Abnormalities
 The hyaloid artery may persist to form a cord or cyst.
 In microphthalmia the eye is too small. (results from intrauterine
infections such as cytomegalovirus).
 Anophthalmia is absence of the eye.
 Congenital aphakia (absence of the lens) and aniridia (absence of
the iris) are rare anomalies.

17. CLINICAL CORRELATES
Eye Abnormalities
 Cyclopia (single eye) and synophthalmia (fusion of the eyes) (comprise a
spectrum of defects in which the eyes are partially or completely fused)
 Blue sclera. (thin sclera through which the pigment of choroid can be
seen).
 Anomalies of pigmentation/ albinism.

18. CLINICAL CORRELATES
Eye Abnormalities
 Retinal detachment—between inner and outer portions of the optic
cup derivatives
 •congenital—failure of fusion
 •acquired—trauma

19. CLINICAL CORRELATES
Eye Abnormalities
Extraocular Muscles… Innervated via CN III, IV, & VI--- Coordinate
movements between the two eyes
Extraocular Muscle Anomalies (congenital):
 Agenesis (single muscle usually)
 Anomalous Attachments (misplaced additional attachments)
 Adherence & Fibrosis Syndromes
 **Failure to align visual axes (strabismus), thus potentially resulting in
diplopia (double-vision) and Amblyopia—reduced/absent visual ability in
one eye “lazy” eye.

20. Summary of various parts of the eye ball
Part Derived from
Lens Surface ectoderm
Retina Neuroectoderm (optic cup)
Vitreous Mesoderm
Choroid Mesoderm (infiltrated by neural crest cells)
Ciliary body Mesoderm
Ciliary muscles Mesenchymal cells covering the developing ciliary body
(neural crest)
Iris Mesoderm
Muscles of the iris Neuroectoderm (from optic cup)
Sclera Mesoderm (infiltrated by neural crest cells?)
Cornea Surface epithelium by ectoderm, substantia propria and
inner epithelium by neural crest
Conjunctiva Surface ectoderm
Blood vessels mesoderm
Optic nerve Neuroectoderm. Its covering (pia, arachnoid and dura)
are derived from mesoderm