Eye: Development

1.Neural Groove- Invaginates to form neural tube, longitudinal, dorsal

2.Optic Plate- thickening from either side of lateral aspect the precursor of forebrain

3. Primary Optic Vesicle-when optic plate grows outwards as a diverticulum towards the surface

4.Optic Cup(secondary optic vesicle)-forms after meeting surface ectoderm, primary optic vesicle invaginates from below

5.Embryonic fissure-the line of invagination during formation of optic cup

6. Inner layer of optic cup- forms main structure of retina-nerve fibres grow from it

7.Outer layer of retina- forms single layer of pigment epithelium

8.The space between retina & pigment epithelium- original primary optic vesicle

9.From anterior border of original optic vesicle develops parts of the ciliary body & iris

10.At the meeting point of neural ectoderm & surface ectoderm, the surface ectoderm thickens to form the lens plate

11.The lens plate invaginates to form lens vesicle & then separates to form lens

12.The hyaloid artery enters the optic cup through embryonic fissure & grows forward to meet the lens, bringing temporary nourishment to the developing structures before it eventually atrophies & disappears-replaced by vitreous-largely secreted by surrounding neural ectoderm

13.The mesoderm surrounding the optic cup differentiates to form the coats of eye & orbital structures, that between the lens & surface ectoderm becomes hollowed to form the anterior chamber, lined by mesodermal condensations which forms the anterior layers of the iris, the angle of anterior chamber & the main structures of cornea.

14.Surface ectoderm remains as corneal & conjunctival epithelium.

15.In the surrounding region, folds grow over in front of the cornea, unite & separate again to to form the lids.

Major Milestones in development of Eye after the Corresponding Periods of Conception:

3wks-Optic groove appears

4th wk-optic pit develops into optic vesicle-lens plate forms-embryonic fissure develops

1month-lens pit & then lens vesicle form-hyaloid vessels develop

11/2 month-closure of embryonic fissure-differentiation of retinal pigment epithelium-proliferation of neural retinal cells-appearance of eyelid folds & nasolacrimal ducts

7th week-formation of embryonic nucleus of lens-sclera begins to form-migration of waves of neural crest(1st wave-corneal & trabecular endothelium,2nd wave-formation of corneal stroma,3rd wave-formation of iris stroma)

3rd month-Differentiation of precursors of rods & cones-anterior chamber appears-fetal nucleus starts developing-sclera condenses-eyelid folds lengthen & fuse

4th month-beginning of formation of retinal vasculature-hyaloid vessel begins to regress-formation of optic disc cup & lamina cribrosa-canal of Schlemm appears-Bowman's membrane develops-formation of major arterial circle & sphincter muscles of iris

5th month-photoreceptors differentiate-eyelid sepration begins

6th month-differentiation of dialator pupillae muscle-nasolacrimal system becomes patent-cones differentiate

7th month-rods differentiate-myelination of optic nerve begins-posterior movement of anterior chamber angle-retinal vessels start reaching nasal peripheri

8th month-completion of anterior chamber angle formation-hyaloid vessels disappear

9th month-retinal vessels reach temporal periphery, pupillary membrane disappears

After Birth-Macular region of the retina develops further

Precursors & Corresponding Derivatives of Eye structures:

Neural Ectoderm- smooth muscle of iris-optic vesicle & cup-iris epithelium-part of vitreous-retina-retinal pigment epithelium,fibres of optic nerve

Surface Ectoderm-conjunctival epithelium,corneal epithelium,lacrimal glands,tarsal glands & lens

Mesoderm-extraocular muscles,corneal stroma,sclera,iris,vascular endothelium of eye & orbit,choroid, part of vitreous

Neural Crest-corneal stroma,keratocytes & endothelium; sclera; trabecular meshwork endothelium, iris stroma, ciliary muscles, choroidal stroma, part of vitreous, uveal & conjunctival melanocytes, meningeal sheaths of optic nerve,ciliary ganglion,Schwann cells of ciliary nerves,orbital bones,orbital connective tissue,connective tissue sheath & muscular layer of ocular & orbital vessels