Eye

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Eye

Development

About the fourth week, optic sulci (optic grooves) develop in the diencephalon. The optic sulci evaginate to form optic vesicles. The optic vesicles enlarge and form hollow optic stalks. The optic vesicles induce the surface ectoderm of the head to form lens placodes. The optic vesicles then invaginate to form double-walled optic cups, and the ventral surfaces of the optic stalks invaginate to form optic fissures. Mesenchyme within each optic cup forms the hyaloid artery and hyaloid vein. In the meantime, the lens placodes have sunk in to form lens pits. The pits detach from the surface ectoderm to form lens vesicles.

The retina is derived from the walls of the optic cups. The proximal parts of the hyaloid vessels form the central artery and vein of the retina. The distal parts of the hyaloid vessels disappear before birth.

Table 16 - Embryonic Contributions to the Eye

Tissue of Origin	Embryonic Structure	Adult Structure
Neuroectoderm of the diencephalon	Optic cup	Retina, iris, ciliary body
Neuroectoderm of the diencephalon	Optic stalk	Optic nerve (CN II)
Surface ectoderm of the head	Lens placode	Lens, anterior epithelium of cornea, Descemet’s membrane
Mesoderm of the head		Sclera, substantia propria of cornea, corneal endothelium, vitreous body, extraocular muscles
	Hyaloid artery and vein	Central artery and vein of retina (branch of ophthalmic artery)
Neural crest cells		Choroid, sphincter pupillae muscle, dilator pupillae muscle, ciliary muscle

Clinical Correlations

Congenital Coloboma

The optic fissure fails to close, causing a cleft in the iris (coloboma of the iris) or the retina (coloboma of the retina).

Microphthalmos

Microphthalmos (“small eye”) commonly results from infectious agents (rubella virus, cytomegalovirus, toxoplasma gondii) or chromosomal abnormalities.

Congenital Cataract

Rubella virus can cause the developing lenses to become opaque, leading to congenital blindness.

Persistent Iridopupillary Membrane

A condition whereby strands of connective tissue cover the pupil at birth.