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
- Prosencephalon
- Mesencephalon
- 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 |
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 | ||||
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 |