Comprehensive Notes in Ophthalmology Chinmaya Sahu
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1GENERAL2

Embryology of the EyeCHAPTER 1

 
EMBRYOLOGY OF THE EYE
The development of the eye occurs in stages.
Immediately, after fertilisation, the embryo goes through blastula, morula and gastrula formation.
The next 3 weeks is the period of embryogenesis. The gastrula further divides to form the ectoderm and the endoderm.
The dorsal part of the ectoderm thickens to form the primitive streak. The ectoderm anterior to the primitive streak is the neuroectoderm.
The cells of the neuroectoderm divide to form the neural tube. By the end of embryogenesis, the neural tube has divided to form
  1. Prosencephalon
  2. Mesencephalon
  3. Rhombencephalon
Prosencephalon further divides to form telencephalon and diencephalon.
From the 4th week on, the period of organogenesis begins.
Optic pit forms as outpounchings from the neural tube between the telencephalon and diencephalon. These enlarge to form the optic vesicle.
When the optic vesicle reaches the surface ectoderm, it thickens to form the lens placode.
In the 4th week, the outer walls of the optic vesicle begin to invaginate to form the optic cup.
The lens placode also invaginates to form the lens vesicle.
Slowly, the optic cup surrounds the lens vesicle.
From the 7th week on, the surrounding paraxial mesoderm and neuroectoderm contribute to the development of the various ocular structures.4
Embryology of the Eye
Eyelid and lacrimal gland and extraocular muscles
Sclera
Cornea
Anterior chamber
22nd day
Optic groove appears
25th day
Optic vesicle forms from optic pit
26th day
Primordia of the superior, inferior, medial rectus and inferior oblique
27th day
Primordia of lateral rectus
28th day
29th day
Primodia of superior oblique
5th week
Osseous structure of the orbit
6th week
Appearance of eyefolds and nasolacrimal duct Ciliary ganglion appears Periocular vasculature starts
Corneal epithelia cells form interconnections
7th week
Sclera begins to form
1st wave neural crest migration: Corneal endothelium 2nd wave of neural crest migration
Corneal stroma
3rd month
Eyefolds lengthen and fuse
Sclera condenses
Limbus appears
AC appears as potential space
4th month
Eyelid glands and cilia form
Formation of lamina cribrosa
Bowman membrane appears
5th month
Eyelid separation begins
6th month
Nasolacrimal duct becomes patent
7th month
Orbicularis muscle differentiation
Posterior movt of AC angle
8th month
9th month After birth
5
Iris and ciliary body
Lens
Vitreous
Retina
Optic nerve
22nd day
Optic groove appears
25th day
Optic vesicle forms from optic pit
26th day
27th day
Formation of lens plate from surface ectoderm
Cells destined to become the retinal pigment epithelium acquire pigmentation
28th day
Embryonic fissure forms
29th day
5th week
Lens pit forms and deepens intothe lens vesicle
Hyaloid vessels develop Primary vitreous develops
6th week
Formation of primary lens fibres
Closure of the embryonic fissure Formation of secondary vitreous
Differentiation of the retinal pigment epithelium Proliferation of neural retinal cells
Movement of ganglion cells towards the optic disc
7th week
1st wave of neural crest migration forms trabecular endothelium
Formation of embryonic nucleus
Formation of tunica vasculosa lentis
Formation of the choroidal vessels from the periocular vasculature
3rd month
Ciliary body appears
Differentiation of the precursors of the rods and retina
4th month
Major arterial circle of the iris develops
Regression of the hyaloid vessels start
Formation of retinal vasculature begins
Formation of physiologic cup of optic disc
Formation of the iris sphincter
Development of longitudinal ciliary muscle and ciliary processes Canal of Schlemm appears
Formation of the tertiary vitreous
6
Iris and ciliary body
Lens
Vitreous
Retina
Optic nerve
5th month
Photoreceptors differentiate
6th month
Differentiation of the dilator pupillae muscle
Cones differentiate Ganglion cells thicken in the macula
7th month
Circular ciliary muscle
Rods differentiate Choroid becomes fibres develop pigmented Migration of the ganglion cells to form the nerve fibre layer of Henle
8th month
Completion of the anterior chamber angle formation
9th month
Pupillary membrane disappears
Retinal vessels reach the temporal periphery
After birth
Development of the macula
Derivatives of Embryonic Tissues
Neuroectoderm
Neural retina,
Retinal pigment epithelium,
Pigmented and non-pigmented ciliary epithelium,
Pigmented iris epithelium,
Sphincter and dilator muscles,
Optic nerve,
Axons and glia,
Cranial
Corneal stroma and endothelium,
Trabecular meshwork,
Ciliary muscles
Neural crest cells
Choroidal stroma
Meningeal sheaths of the optic nerve
Ciliary ganglion
Orbital bones (all midline)
Connective tissue of the orbit, Muscular layer and connective tissue sheath of all the ocular and orbital blood vessels
Surface ectoderm
Epithelium, glands, cilia of the skin covering lids
Conjunctival epithelium, Lacrimal gland, Lacrimal drainage system,
Corneal epithelium, Lens
Mesoderm
Fibres of the extraocular muscles, Endothelial lining of all orbital and ocular blood vessels, Temporal portion of sclera, Vitreous