Eye: optic vesicle, optic cup and lens !

Process

The eye starts as an outgrowth of the brain that touches the embryo's skin and makes it form the lens.

Updated 2026-11-01

See it in 3D: Lens · Retina · Optic nerve · Cornea · Iris · Ciliary body · Choroid · Sclera · Vitreous · Central retinal artery · Eyelids

What it is

The eye forms through interaction between an outgrowth of the diencephalon (the optic vesicle), the surface ectoderm that forms the lens, and mesenchyme, largely neural crest. The optic cup becomes the retina, the stalk becomes the optic nerve, and a groove underneath carries the hyaloid vessels. Knowing which layer comes from which germ layer explains coloboma, aniridia and congenital cataract.

Key facts

Day 22: optic grooves appear in the neural folds of the forebrain.
End of week 4: the optic vesicles touch the ectoderm and induce the lens placode.
Week 5: the lens vesicle separates from the ectoderm and sits in the mouth of the optic cup.
Week 7: the choroid (optic) fissure closes; failure causes coloboma.
Hyaloid artery: its proximal part becomes the central retinal artery; the distal part regresses, leaving the hyaloid canal.
Eyelids: they fuse near the end of the embryonic period and reopen around weeks 26–28.

Structure

Neuroectoderm (optic cup): neural retina (inner layer), pigment epithelium (outer layer), iris and ciliary epithelium, sphincter and dilator pupillae muscles.
Surface ectoderm: lens, corneal epithelium, conjunctiva, lacrimal gland.
Neural crest: corneal stroma and endothelium, iris stroma, ciliary muscle, sclera.
Mesoderm: extraocular muscles and vascular endothelium; the choroid receives mesoderm and crest.

Step by step

PAX6 marks a single eye field in the neural plate.
SHH from the prechordal plate splits the field into two optic primordia.
The optic vesicle grows out of the diencephalon and touches the surface ectoderm.
The ectoderm thickens into a placode and invaginates as the lens vesicle.
The optic vesicle folds into a double-walled cup; underneath lies the choroid fissure with the hyaloid artery.
The fissure closes in week 7 and the mouth of the cup becomes the pupil.
The optic stalk fills with retinal axons and becomes the optic nerve.
Mesenchyme forms the choroid, sclera, corneal stroma and iris stroma.

Markers

PAX6
PAX2
SHH
SOX2
MITF
BMP4

Clinical notes

Coloboma: incomplete closure of the choroid fissure in week 7.
Aniridia: PAX6 mutations.
Cyclopia: the eye field does not split for lack of SHH (holoprosencephaly).
Rubella in weeks 4–7: congenital cataract, because the lens forms then.
Persistent pupillary membrane or hyaloid artery remnants.

Test yourself

Think of the answer, then tap the question to see it.

Which germ layer does the lens come from?

Surface ectoderm, induced by the optic vesicle.

Which structure closes in week 7, and what does its failure cause?

The choroid (optic) fissure; if it fails to close, a coloboma remains.

Where do the sphincter and dilator pupillae muscles come from?

From the neuroectoderm at the rim of the optic cup, not from mesoderm.

What remains of the hyaloid artery in the adult?

Its proximal part is the central retinal artery; the distal part disappears, leaving the hyaloid canal.

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See it in 3D

The structures of Durgical's 3D anatomy where it is found.

Cataract

← All of embryology

Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.

Sources: Embryology of the Eye and Ocular Adnexa (American Academy of Ophthalmology (EyeWiki), 2024); Coloboma: MedlinePlus Genetics (U.S. National Library of Medicine, 2024); Langman's Medical Embryology, 13th ed., ch. 20: Eye (Wolters Kluwer, 2015).

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Representative model, for educational purposes only.