Eye
Ass. Prof. Dr. Malak A. Al-yawer
Optic Cup and Lens Vesicle
The optic vesicles.
Double-walled optic cup
Shortly thereafter the optic vesicle begins to invaginate and forms the double-walled optic cup .
Intraretinal space
The inner and outer layers of this cup are initially separated by a lumen, the intraretinal space (B) but soon this lumen disappears, and the two layers appose each other
The choroid fissure
Lens vesicle
During these events, cells of the surface ectoderm, initially in contact with the optic vesicle, 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
Retina, Iris, and Ciliary Body
Pigmented layer of the retina
The outer layer of the optic cup, which is characterized by small pigment granules, is known as the pigmented layer of the retina.
Neural layer of the optic cup
Development of the inner (neural) layer of the optic cup is more complicated. Pars optica retinae pars ceca retinae
Pars optica retinae
the photoreceptive layer, mantle layer, fibrous layerPars optica retinae
The posterior four-fifths of the neural layer
the photoreceptive layer, mantle layer, fibrous layer
Pars optica retinae photoreceptive layer
contains cells bordering the intraretinal space that differentiate into light-receptive elements, rods and conesPars optica retinae the mantle layer
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
Pars optica retinae fibrous layer
The pars ceca retinae
pars iridica retinae pars ciliaris retinae
The pars ceca retinae
It is the anterior fifth of the inner layer It 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.
pars iridica retinae
The region between the optic cup and the overlying surface epithelium
is filled with loose mesenchyme. The sphincter and dilator pupillae muscles form in this tissue. These muscles develop from the underlying ectoderm of the optic cup.
The iris
In the adult, is formed by the pigment-containing external layer, the unpigmented internal layer of the optic cup, and a layer of richly vascularized connective tissue that contains the pupillary muscles (
The pars ciliaris retinae
The pars ciliaris retinae
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
Growth of the lens
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 since new (secondary) lens fibers are continuously added to the central core.
Choroid, Sclera, and Cornea
At the end of the fifth week, the eye primordium
Differentiation of mesenchymal layers overlying the anterior aspect of the eye is different
Hence, the cornea is formed by
Vitreous Body
Vitreous Body
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.
Optic Nerve
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 neuroglia that 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.
Clinical Correlates
Eye Abnormalities
Coloboma
The iridopupillary membrane
may persist instead of being resorbed during formation of the anterior chamber.
Congenital cataracts
the lens becomes opaque during intrauterine life. this anomaly is usually genetically determined
The hyaloid artery may persist to form a cord or cyst. Normally, the distal portion of this vessel degenerates, leaving the proximal part to form the central artery of the retina.
Congenital aphakia (absence of the lens) and ) aniridia (absence of the iris) are rare anomalies
Anophthalmia
is absence of the eye. In some cases, histological analysis reveals some ocular tissue. The defect is usually accompanied by severe cranial abnormalities.
Cyclopia synophthalmia
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