Eye

I. DEVELOPMENT OF THE OPTIC VESICLE (Figure 141). The optic vesicle begins to develop at day 22 with the formation of the optic sulcus. The optic sulcus evaginates from the wall of the diencephalon as the optic vesicle, consisting of neuroectoderm. The optic vesicle invaginates and forms a double-layered optic cup and optic stalk.

A. The optic cup and its derivatives (Table 14-1). The double-layered optic cup consists of an outer pigment layer and an inner neural layer.

1. Retina a. The outer pigment layer of the optic cup gives rise to the pigment layer of the retina.

b. The intraretinal space separates the pigment layer of the retina from the neural layer of the retina. Although the intraretinal space is obliterated in the adult, it remains a weakened area prone to retinal detachment.

C. The inner neural layer of the optic cup gives rise to the neural layer of the retina (i.e., the rods and cones, bipolar cells, and the ganglion cells).

a. The epithelium of the iris develops from the anterior portions of both the outer pigment layer and the inner neural layer of the optic cup, which explains its histologic appearance of two layers of columnar epithelium.

b. The stroma of the iris develops from mesoderm continuous with the choroid.

C. The iris contains the dilator pupillae muscle and the sphincter pupillae muscle, which are formed from the epithelium of the outer pigment layer by a transformation of these epithelial cells into contractile cells.

3. Ciliary body (see Figure 14-2)

a. The epithelium of the ciliary body develops from the anterior portions of both the outer pigment layer and the inner neural layer of the optic cup, which explains its histologic appearance of two layers of columnar epithelium.

b. The stroma of the ciliary body develops from mesoderm continuous with the choroid.

C. The ciliary body contains the ciliary muscle, which is formed from mesoderm within the choroid.

d. Ciliary processes are components of the ciliary body.

(1) 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.

(2) The ciliary processes give rise to the suspensory fibers of the lens (ciliary zonule), which suspend the lens.

Optic Nerve Development Optic Stalk
Dicnccphalon Lens placode Optic cup Optic stalk

Ciliary body

Vitreous body

Sclera

Choroid

Retina

Iris

Cornea (3 layers)

Iridopupillary membrane

Coroid Fissure Hyloid Artry

Central artery of retina

Dura

Pia-arachnoid Optic nerve (CNII)

Extraocular muscle

Figure 14-1. (A) The optic cup and optic stalk are evaginations of the diencephalon. The optic cup induces surface ectoderm to differentiate into the lens placode. (B) Formation of the optic nerve (CN 11) from the optic stalk. The choroid fissure, which is located on the undersurface of the optic stalk, permirs access of the hyaloid artery and vein to the inner aspect of the eye. The choroid fissure eventually closes. As ganglion cells form in the retina, axons accumulate in the optic stalk and cause the inner and outer layers of the optic stalk to fuse, obliterating the lumen (or intraretinal space) and forming the optic nerve. (C) The adult eye. Note that the sclera is continuous with the dura mater and the choroid is continuous with the pia-arachnoid. The iridopupillary membrane is normally obliterated. (Adapted from Dudek RW, Fix JD: BRS Embryology, 2nd ed. Baltimore, Williams & Wilkins, 1998, p 114.)

Optic cup

Lumen of the optic stalk

Optic Stalk And Choroidal Fissure

Choroid fissure closure

Choroid fissure

Optic stalk

Axons from retina ganglion cells

Central artery and vein of retina.

Optic nerve (CN II)

Optic cup

Lumen of the optic stalk

Axons from retina ganglion cells

Central artery and vein of retina.

Optic nerve (CN II)

Iris

Cornea (3 layers)

Iridopupillary membrane

Extraocular muscle

Choroid fissure

Choroid fissure closure

Ciliary body

Vitreous body

Sclera

Choroid

Retina

Central artery of retina

Dura

Pia-arachnoid Optic nerve (CNII)

Optic stalk

Outer and inner layers of the optic stalk

Figure 14-1. (A) The optic cup and optic stalk are evaginations of the diencephalon. The optic cup induces surface ectoderm to differentiate into the lens placode. (B) Formation of the optic nerve (CN 11) from the optic stalk. The choroid fissure, which is located on the undersurface of the optic stalk, permirs access of the hyaloid artery and vein to the inner aspect of the eye. The choroid fissure eventually closes. As ganglion cells form in the retina, axons accumulate in the optic stalk and cause the inner and outer layers of the optic stalk to fuse, obliterating the lumen (or intraretinal space) and forming the optic nerve. (C) The adult eye. Note that the sclera is continuous with the dura mater and the choroid is continuous with the pia-arachnoid. The iridopupillary membrane is normally obliterated. (Adapted from Dudek RW, Fix JD: BRS Embryology, 2nd ed. Baltimore, Williams & Wilkins, 1998, p 114.)

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