Jittipan Chavadej, Ph.D. Anatomy Department,Fac. of Science Mahidol University yr. 2000

Mature structures of the eye *Eyeball - cornea & sclera - lens, eye chamber - retina, optic nerve *Surrounding muscular structure - ciliary body - iris muscles - extraocular muscles&conjunctiva

Structure of the eye

Formation of the eye  Are formed by 3 different germ layers. 1. Neuroectoderm 2. Surface ectoderm 3. Mesoderm

1Neuroectoderm - forebrain(dien.) --> - retina & optic nerve - iris & ciliary body 1Surface ectoderm - above optic vesicle --> lens & cornea 1Mesoderm -all CNT & vascular structures --> choroid layer & sclera

Retina & Optic nerve form from optic vesicle Diagram showing the formation of optic vesicle & the lens placode

Ventrolateral view off the optic cup & optic stalk showing the hyaloid artery in the choroid fissure

Retina formation cChanges of inner layer of optic cup (lens & cornea) neural retina Epith. cells neurons & light photoreceptor cells (rods&cones) Thickeningdifferentiation bOuter layer of optic cup (thin) pigment layer of the retina

*Neural retina (multilayers) consists of- rods & cones - bipolar neurons in inner nuclear layer - ganglion cells in ganglion cell layer 1 st- ganglion cell--> optic nerve 2 nd- bipolar neurons & rods - cones /Differentiation

Diagram showing the differentiation of layers of the neural retina. Optic nerve/stalk

Diagram showing the development of the layers of the neural retina

Formation of lens Surface ectoderm lens placodes lens vesicles lens Differentiation of the lens elongation of lens fiber contain large amount of crystallin proteins - alpha,beta & gamma (mol.level)

Invagination Lens cup Lens vesicle Elongation of 1 0 fiber Embryonic lens Alpha(+/-) Crystallin(n o) Alpha(++) Beta(+/-) Gamma(+/-) Alpha(+++) Beta(+++) Gamma(+++) Alpha(++) Beta(++) Gamma(+)

Anteroposterior section of the eye showing optic cup, optic stalk and lens vesicle

Formation of cornea  2 sources-*surface ectoderm  Inductive influence of the lens -surface ectoderm- primary stroma : collagen type I, II, IX -neural crest cells- corneal endothelium & secondary stroma (hyaluronic acid-hyaluronidase)

Anteroposterior section through the eye.

Final developmental changes of cornea= Formation of transparency -by removing water from secondary stroma (40%) -degradation of hyaluronic acid -thyroxine--> corneal endothelium - by pumping sodium into ant r chamber of the eye

Iris & Ciliary body formation -at the lip of optic cup *Ciliary body -muscle containing structure + suspensory ligament of the lens (radial set of muscle) --> modulate shape of the lens *Iris -2 sets of muscle (sphincter & dilator pupillae) -->control the amt of light passing through the lens

Development of the iris and the ciliary body.The rim of the optic cup is covered by the mesenchyme, in which the sphinter and dilator pupillae develop from the underlying ectoderm.

Choroid coat and sclera Origin = a layer of mesenchymal cells + neural crest cells outside the optic cup- under influence of the pigmented epith. of the retina Choroid coat-a highly vascular tunic Sclera-dense collageneous covering -tough outer coat of the eye

Diagram showing the development of the choroid & the sclera

Vitreous body & Hyaloid artery Vitreous body- loose mesenchyme forming a loose fibrillar mesh along with a gelatinous substance in optic cup Hyaloid artery- enter the eyeball through the choroid fissure of the optic stalk-->retina,vitreous body -->post r wall of the lens

Note :ant r chamber,vitreous cavity-vitreous body

,Regression of hyaloid artery (in the vitreous body),Persistance of prox. part of hyaloid artery as central artery of the retina Changes of Hyaloid artery

A B C Stages in development and regression of the hyaloid artery in the embryonic eye

Eyelid and Lacrimal gland /7 th wk. - fold of skin /9 th wk. - meet & temporary fusion /6 th mo. -loosening of epith. union /7 th mo. - reopening of the eyelid

Conjunctival sac - space betw. the front of eyeball & eyelid Lacrimal gl.-multiple epithelial bud from lateral surface ectoderm -nasolacrimal duct -begin to function~6 wk. after birth

Note : eyelid,iridopupillary membrane & conjunctival sac

Congenital malformations of the eye 2 Anophthalmos -absence of an eye 2 Microphthalmos -smaller than normal 2 Coloboma iridis -nonclosure of choroid fissure of the iris