Optic Nerve Embryology

Ciliary muscles

Iris Dilator And Sphincter

Ciliary process

"Outer pigmented layer of iris

Inner unpigmented layer of iris

Figure 17.6 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.

Dilator pupillae Sphincter pupillae

Ciliary process

"Outer pigmented layer of iris

Inner unpigmented layer of iris

Figure 17.6 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.

Sclera Dura Choroid Pia
Figure 17.7 Section through the eye of a 15-week fetus showing the anterior chamber, iridopupillary membrane, inner and outer vascular layers, choroid, and sclera.

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 (Fig. 17.7).

Differentiation of mesenchymal layers overlying the anterior aspect of the eye is different. The anterior chamber forms through vacuolization and splits the mesenchyme into an inner layer in front of the lens and iris, the iridopupil-lary membrane, and an outer layer continuous with the sclera, the substantia propria of the cornea (Fig. 17.7). The anterior chamber itself is lined by flattened mesenchymal cells. Hence, the cornea is formed by (a) an epithelial layer derived from the surface ectoderm, (b) the substantia propria or stroma, which is continuous with the sclera, and (c) an epithelial layer, which borders the anterior chamber. The iridopupillary membrane in front of the lens disappears completely, providing communication between the anterior and posterior eye chambers.

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