1. During the 5th week of development, the optic cup begins to invaginate from the optic vesicles and forms the double-walled optic cup with inner and outer layers. The lens placode also begins to form from surface ectoderm. 2. By the 7th week, the choroid fissure has closed and the optic cup forms the round opening of the future pupil. The lens placode has invaginated to form the lens vesicle. 3. Various structures develop from the layers of the optic cup, including the neural retina from the inner layer and the pigmented retina and iris from the outer layer. The iris muscles and ciliary body also begin to form at this stage

1. EMBRYLOGY BY DR. THAAER MAOHAMMED DAHER ALSAADM.B.Ch.B. (MBBS) F.I.B.M.S. (PhD)SPECIALIST IN GENERAL SURGERYSENIOR LECTURERIMS MSU

2. Eye DEVELOPMENT

3. Optic Cup and Lens Vesicle 1/2 The developing eye appears in the 22-day embryo as a pair of shallow grooves on the sides of the forebrain. With closure of the neural tube, these grooves form outpocketings of the forebrain, the optic vesicles. The optic vesicle begins to invaginate and forms the double-walled optic cup. The inner and outer layers of this cup are initially separated by a lumen, the intraretinalspace, This lumen disappears, and the two layers appose each other. Invagination is not restricted to the central portion of the cup but also involves a part of the inferior surface that forms the choroid fissure. Formation of this fissure allows the hyaloid artery to reach the inner chamber of the eye.

4. A. Transverse section through the forebrain of a 22-day embryo (approximately 14 somites), showing the optic grooves B. Transverse section through the forebrain of a 4-week embryo showing the optic vesicles in contact with the surface ectoderm. Note the slight thickening of the ectoderm (lens placode). C. Transverse section through the forebrain of a 5-mm embryo showing invagination of the optic vesicle and the lens placode

5. M H D. Scanning electron micrograph showing a frontal view of a mouse E. Scanning electron micrograph of a mouse embryo during formation of the optic vesicle. The embryo has been cut sagittally to reveal the inside of the brain vesicles and outpocketing of the optic vesicle (arrow) from the forebrain. H, hindbrain; and M, midbrain.

6. A. The forming lens vesicle, not entirely closed; the two layers of the optic cup; and the lumen (L) of the optic stalk. (B) 7 weeks in the human B. Lens fibers (Lf ) and neural (N) and pigment layers (arrow) forming Scanning electron micrographs of sections through the eyes of mouse embryos at stages equivalent to (A) 6 weeks (b) 7 weeks

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

8. Section through the eye of a 15-week fetus showing the anterior chamber, iridopupillary membrane, inner and outer vascular layers, choroid, and sclera

9. . B. Seventh week (15 mm). C. Ninth week A. Sixth week (9 mm). Transformation of the optic stalk into the optic nerve. Note the central artery of the retina in the optic nerve.

10. A. Coloboma iris. B. Persistence of the iridopupillary membrane.

11. During the seventh week, The lips of the choroid fissure fuse, The mouth of the optic cup becomes a round opening, the future pupil. The cells of the surface ectoderm begin to elongate and form the lens placode. This placode subsequently invaginates and develops into the lens vesicle. During the fifth week, the lens vesicle loses contact with the surface ectoderm and lies in the mouth of the optic cup. Optic Cup and Lens Vesicle 2/2

12. Section through the eye of a 15-week fetus showing the anterior chamber, iridopupillary membrane, inner and outer vascular layers, choroid, and sclera

13. Retina, Iris, and Ciliary Body 1/4 The outer layer of the optic cup is known as the pigmented layer of the retina. Development of the inner (neural) layer of the optic cup is more complicated. The posterior four-fifths, the pars optica retinae, contains cells bordering the intraretinal space that differentiate into light-receptive elements, rods and cones. Adjacent to this photoreceptive layer is the mantle layer, which, as in the brain, gives rise to neurons and supporting cells, including the outer nuclear layer, inner nuclear layer, and ganglion cell layer.

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

15. The optic stalk develops into the optic nerve. The anterior fifth of the inner layer, the pars ceca retinae, remains one cell layer thick. It later divides into the pars iridica retinae, which forms the inner layer of the iris, and the pars ciliaris retinae, which participates in formation of the ciliary body. The region between the optic cup and the overlying surface epithelium is filled with loose mesenchyme. Retina, Iris, and Ciliary Body 2/4

16. Thesphincter and dilator pupillae muscles form in this tissue. These muscles develop from the underlying ectoderm of the optic cup. In the adult, the iris is formed by the pigment-containing external layer, the unpigmentedinternal layer of the optic cup, and a layer of richly vascularized connective tissue that contains the pupillary muscles. Retina, Iris, and Ciliary Body 3/4

17. The pars ciliaris retinae is easily recognized by its marked folding. Externally it is covered by a layer of mesenchyme thatforms the ciliary muscle; on the inside it is connected to the lens by a network of elastic fibers, the suspensory ligament or zonula. Contraction of the ciliary muscle changes tension in the ligament and controls curvature of the lens. Retina, Iris, and Ciliary Body 4/4

18. Lens Shortly after formation of the lens vesicle, cells of the posterior wall begin to elongate anteriorly and form long fibers that gradually fill the lumen of the vesicle. By the end of the seventh week, these primary lens fibers reach the anterior wall of the lens vesicle. Growth of the lens is not finished at this stage, New (secondary) lens fibers are continuously added to the central core.

19. Section through the eye of a 15-week fetus showing the anterior chamber, iridopupillary membrane, inner and outer vascular layers, choroid, and sclera

20. Choroid, Sclera, and Cornea 1/2 At the end of the fifth week, The eye primordium is completely surrounded by loose mesenchyme. This tissue soon differentiates into an inner layer comparable with the pia mater of the brain and an outer layer comparable with the dura mater. The inner layer later forms a highly vascularized pigmented layer known as the choroid; The outer layer develops into the sclera and is continuous with the dura mater around the optic nerve.

22. Vitreous Body Mesenchyme not only surrounds the eye primordium from the outside but also invadesthe inside of the optic cup by way of the choroid fissure. Here it forms the hyaloid vessels, which during intrauterine life supply the lens and form the vascular layer on the inner surface of the retina. In addition, it forms a delicate network of fibers between the lens and retina. The interstitial spaces of this network later fill with a transparent gelatinous substance, forming the vitreous body. The hyaloid vessels in this region are obliterated and disappear during fetal life, leaving behind the hyaloid canal.

23. Optic Nerve The optic cup is connected to the brain by the optic stalk, which has a groove, the choroid fissure, on its ventral surface. In this groove are the hyaloid vessels. The nerve fibers of the retina returning to the brain lie among cells of the inner wall of the stalk. During the seventh week, The choroid fissure closes, and a narrow tunnel forms inside the optic stalk. As a result of the continuously increasing number of nerve fibers, the inner wall of the stalk grows, and the inside and outside walls of the stalk fuse. Cells of the inner layer provide a network of neurogliathat support the optic nerve fibers. The optic stalk is thus transformed into the optic nerve. Its center contains a portion of the hyaloid artery, later called the central artery of the retina. On the outside, a continuation of the choroid and sclera, the pia arachnoid and dura layer of the nerve, respectively, surround the optic nerve.

24. . B. Seventh week (15 mm). C. Ninth week A. Sixth week (9 mm). Transformation of the optic stalk into the optic nerve. Note the central artery of the retina in the optic nerve.

25. C L I N I C A L C O R R E L A T E SEye Abnormalities 1/2 Coloboma may occur if the choroid fissure fails to close. (Normally this fissure closes during the seventh week of development). Coloboma iridis. Coloboma is a common eye abnormality frequently associated with other eye defects. Colobomas(clefts) of the eyelids may also occur. The iridopupillary membrane (Fig. 17.11B) may persist instead of being resorbed during formation of the anterior chamber. In congenital cataracts the lens becomes opaque during intrauterine life. Although this anomaly is usually genetically determined, many children of mothers who have had German measles (rubella) between the fourth and seventh weeks of pregnancy have cataracts. (If the mother is infected after the seventh week of pregnancy, the lens escapes damage, but the child may be deaf as a result of abnormalities of the cochlea)

26. The hyaloid artery may persist to form a cord or cyst. In microphthalmia the eye is too small. (results from intrauterine infections such as cytomegalovirus). Anophthalmia is absence of the eye. Congenital aphakia (absence of the lens) and aniridia (absence of the iris) are rare anomalies. Cyclopia (single eye) and synophthalmia (fusion of the eyes) (comprise a spectrum of defects in which the eyes are partially or completely fused), (these defects are invariably associated with cranial defects, such as holoprosencephaly, in which the cerebral hemispheres are partially or completely merged into a single telencephalic vesicle). Blue sclera. (thin sclera through which the pigment of choroid can be seen). Anomalies of pigmentation/ albinism. C L I N I C A L C O R R E L A T E SEye Abnormalities 2/2

27. Summary of various part of the eye ball.

29. Craniopharyngioma is a peculiar tumor of the remnant of the Rathke’s pouch.

30. Accessory anterior lobe may be seen in relation to the posterior wall of the pharynx.

32. Adrenal Gland The adrenal gland consists of a superficial cortex and a deeper medulla. The cells of the cortex arise from coelomic epithelium (mesoderm). The cells of the medulla are derived from the neural crest (ectoderm). Chromaffin tissue is made up of cells similar to those of the adrenal medulla and derived from the cells of the neural crest. (this tissue is related to the abdominal aorta, also seen in relation to sympathetic ganglia and plexuses and along the splanchnic nerves). The cells of the coelomic epithelium may be divided into two groups: Fetal cortex – disappear after birth. Defenitive cortex.

33. Anomalies of Adrenal Gland Ectopic adrenal cortical tissue. Ectopic Adrenal gland. Congenital hyperplasia; In male it leads to Adrenogenital syndrome. In female it leads to pseudohermaphroditism.