Development of the Eye

Early Development

• Week 3
  • The notochord appears in the mesoderm.
  • Notochord secretes growth factors.
  • Stimulates differentiation of ectoderm into neuroectoderm.
  • Forms neural plate, which thickens.
• Neurulation
  • Neural folds form from the lateral edges of the neural plate.
  • Neural folds fuse midline to create the neural tube.
  • Neural tube is the precursor to the brain and spinal cord.
  • Completed by end of week 4.

Week 5 Developments

• Swellings appear at cranial end of neural tube.
• Formation of three primitive vesicles:
  • Prosencephalon (divides into telencephalon and diencephalon).
  • Mesencephalon
  • Rhombencephalon (divides into metencephalon and myelencephalon).
• Diencephalon Development
  • Forms a thickened area on either side.
  • Depression forms the optic sulcus.
  • Optic sulcus enlarges into optic vesicle, proximal area forms optic stalk.

Formation of Eye Structures

• Optic Vesicle
  • Grows laterally, contacts surface ectoderm.
  • Surface ectoderm thickens into lens placode.
  • Lens placode forms lens vesicle, which detaches and invaginates into optic vesicle.
  • Optic vesicle becomes optic cup, with a notable deficiency called the choroidal fissure.

Mesenchyme and Eye Formation

• Mesenchyme Layers
  • Surrounds developing neural tube and optic vesicle.
  • Outer Fibrous Layer: Forms dura mater, cornea (with layers from fibrous mesenchyme), sclera, and extraocular muscles.
  • Inner Vascular Layer: Forms arachnoid mater, pia mater, choroid, and ciliary body.

Retina Development

• Retina Layers
  • Outer Pigmented Layer: Derived from outer optic cup wall; becomes pigmented epithelium of retina, ciliary body, and iris.
  • Inner Neural Layer: Derived from inner optic cup wall; divides into matrix, mantle, and marginal layers.
  • Roles:
    • Matrix Layer: Forms rods and cones (photoreceptors).
    • Mantle Layer: Forms bipolar cells, ganglion cells, and supporting tissues.
    • Marginal Layer: Forms ganglion cells, nerve fibers, optic nerve.

Additional Eye Structures

• Ciliary Body
  • Stroma, muscles, and blood vessels from vascular mesenchyme, epithelium from optic cup.
• Iris
  • Stroma and blood vessels from vascular mesenchyme, sphincter pupilli, and dilator pupilli muscles from neuroectoderm of optic cup.
• Eyelids and Conjunctiva
  • Develop from surface ectoderm.

Lens Development

• Lens Vesicle Formation
  • Neural retina signals elongation of cells to form primary lens fibers.
  • Synthesis of crystallines is induced, contributing to transparency.
  • Lens grows post-birth with new secondary fibers from equatorial cells in the germinative zone.