CLASS NOTES EYE DEVELOPMENT PRESENTATION.pptx

Development of the Eye

1. Ocular embryology CLASS NOTES

2. The development of the optic vesicle This b egins at day 22 with the formation of optic sulcus It is an evagination from the wall of the diencephalon, consisting of neuroectoderm. The optic vesicle invaginates and forms a double-layered optic cup and optic stalk. PAX6 is the master homeotic gene in eye development. PAX6 is expressed predominately in the optic cup and lens placode. PAX2 is expressed predominately in the optic stalk. SHH- Division of eyeball into two. Cyclopean eye-Syn opthalmia - Proboscis

3. The optic cup and its derivatives . The double-layered optic cup consists of an outer pigment layer and an inner neural layer. Retina The outer pigment layer of the optic cup gives rise to the pigment layer of the retina. The intraretinal space separates the outer pigment layer from the inner neural layer. Although the intraretinal space is obliterated in the adult, it remains a weakened area prone to retinal detachment. The inner neural layer of the otic cup gives rise to the neural layer of the retina (i.e., the rods and cones, bipolar cells, ganglion cells, etc.).

4. Iris The epithelium of the iris develops from the anterior portions of both the outer pigment layer and inner neural layer of the optic cup, which explains its histological appearance of two layers of columnar epithelium. The stroma develops from mesoderm continuous with the choroid. The iris contains the dilator pupillae muscle and sphincter pupillae muscle, which are formed from the epithelium of the outer pigment layer by a transformation of these epithelial cells into contractile cells.

5. Ciliary body The epithelium of the ciliary body develops from the anterior portions of both the outer pigment layer and inner neural layer of the optic cup, which explains its histological appearance of two layers of columnar epithelium. The stroma develops from mesoderm continuous with the choroid. The ciliary body contains the ciliary muscle, which is formed from mesoderm within the choroid. The ciliary processes are components of the ciliary body.

6. The ciliary processes produce aqueous humor, which circulates through the posterior and anterior chambers and drains into the venous circulation via the trabecular meshwork and the canal of Schlemm. The ciliary processes give rise to the suspensory fibers of the lens (ciliary zonule),which are attached to and suspend the lens

7. The optic stalk and its derivatives The optic stalk contains the choroid fissure, in which the hyaloid artery and vein are found. The hyaloid artery and vein later become the central artery and vein of the retina. The optic stalk contains axons from the ganglion cell layer of the retina. The choroid fissure closes during week 7, so that the optic stalk, together with the axons of the ganglion cells, forms the optic nerve (CN II), optic chiasm, and optic tract.

8. The optic nerve (CN II) is a tract of the diencephalon and has the following characteristics: The optic nerve is not completely myelinated until 3 months after birth It is myelinated by oligodendrocytes. The optic nerve is not capable of regeneration after transection. The optic nerve is invested by the meninges and therefore is surrounded by a subarachnoid space, which plays a role in papilledema

9. Development of other eye structures Sclera. The sclera develops from mesoderm surrounding the optic cup. The sclera forms an outer fibrous layer that is continuous with the dura mater posteriorly and the cornea anteriorly. Choroid. The choroids develop from mesoderm surrounding the optic cup. The choroids form a vascular layer that is continuous with the pia/arachnoid posteriorly and iris/ciliary body anteriorly.

10. Anterior chamber The anterior chamber develops from mesoderm over the anterior aspect of the eye that is continuous with the sclera and undergoes vacuolization to form a chamber. The anterior chamber essentially splits the mesoderm into two layers: The mesoderm posterior to the anterior chamber is called the iridopupillary membrane, which is normally resorbed prior to birth. The mesoderm anterior to the anterior chamber develops into the substantia propria of the cornea and corneal endothelium.

11. Cornea The cornea develops from both surface ectoderm and mesoderm lying anterior to the anterior chamber. The surface ectoderm forms the anterior epithelium of the cornea. The mesoderm forms the substantia propria of the cornea (i.e., Bowman layer, stroma, and Descemet membrane) and corneal endothelium.

12. Lens The lens develops from surface ectoderm, which forms the lens placode. The lens placode invaginates to form the lens vesicle. The adult lens is completely surrounded by a lens capsule. The lens epithelium is a simple cuboidal epithelium located beneath the capsule only on the anterior surface. The lens epithelium is mitotically active and migrates to the equatorial region of the lens.

13. The lens fibers are prismatic remnants of the lens epithelium that lose their nuclei and organelles. The lens fibers are filled with cytoskeletal proteins called filensin and crystallin,which maintain the conformation and transparency of the lens.

14. Vitreous body . The vitreous body develops from mesoderm that migrates through the choroid fissure and forms a transparent gelatinous substance between the lens and retina. It contains the hyaloid artery, which is later obliterated to form the hyaloid canal of the adult eye.

15. Canal of Schlemm. The canal of Schlemm is found at the sclero corneal junction called the limbus and drains the aqueous humor into the venous circulation. An obstruction of the canal of Schlemm results in increased intraocular pressure (glaucoma). Extraocular muscles . The extraocular muscles develop from mesoderm of somitomeres 1, 2, and 3 (also called preotic myotomes) that surround the optic cup.

16. Embryonic Eye Structures and Their Adult Derivatives Diencephalon (neuroectoderm) Optic cup Retina, iris epithelium, dilator and sphincter pupillae muscles of iris, ciliary body epithelium Optic stalk Optic nerve (CN II), optic chiasm, optic tract Surface ectoderm Lens, anterior epithelium of cornea, bulbar and palpebral conjunctiva

17. Mesoderm Sclera, choroid, stroma of iris, stroma of ciliary body, ciliary muscle, substantia propria of cornea, corneal endothelium, vitreous body, central artery and vein of retina, extraocular muscle