Embryology

• Germinal Cell Layers


  • ECTODERM-neural tissue, skin, nails, hair
  • MESODERM-muscle, bone, connective tissue, circulatory system
  • ENDODERM-internal organs
• Eyes develop from the Diencephalon
• Brain Regions


  • Telencephalon (forebrain)
  • Diencephalon
  • Mesencephalon (midbrain)
  • Metencephalon
  • Myelencephalon (hindbrain)
• Spinal cord develops from the Rhombencephalon (hindbrain)
• Germinal Cell Layers


  • Ectoderm (outer)
  • Mesoderm (middle)
  • Endoderm (inner)
• Ectoderm


  Gives rise to neural tissue, skin, nails, hair
• Mesoderm

  Gives rise to muscle, bone, connective tissue, circulatory system
• Endoderm


  Gives rise to internal organs
• Formation of neural plate (neuroectoderm)

  1. Ectoderm thickens and differentiates

  2. Invaginates to form neural tube

  3. Neural crest cells migrate in
• Contributions to Ocular Development


  • ECTODERM: Surface ectoderm, neuroectoderm, neural crest cells
  • MESODERM: Mesenchyme
  • ENDODERM: No contribution to ocular development
• Optic Cup & Lens Vesicle


  1. Day 22 - first event in development of the eye

  2. Optic primordium appears in neural fold

  3. Optic stalk and vesicles form

  4. Meet surface ectoderm

  5. Induces surface ectoderm thickening called lens placode

  6. Lens placode and optic vesicle invaginate to form lens vesicle and optic cup
• Optic Cup


  • Has thick inner layer and thinner outer layer
  • Outer layer becomes RPE
  • Inner layer becomes NSR
• The first event in ocular development is at 22 days
• The optic vesicle meets the surface ectoderm, which induces it to thicken and form lens placode
• Lens Vesicle and Optic Cup Formation


  1. Lens placode invaginates to form lens vesicle

  2. Invagination of the optic vesicle forms the optic cup
• The choroidal fissure forms
• Hyaloid artery provides lens blood supply
• Degeneration of the hyaloid artery


  As eye development progresses, the hyaloid arteries eventually regress
• Development of the Retina

  • The neurosensory retina (NSR) develops from the inner layer of the optic cup
  • The anterior 1/5 of the inner layer that overlaps the lens does NOT develop into nervous tissue
  • The posterior 4/5 develop into the NSR
  • The demarcation between the anterior 1/5 and posterior 4/5 is visible in the adult eye as the ora serrata
• Macular and Foveal Development

  1. Macular development starts at 4.5 months

  2. Ganglion cell increases temporal to the optic disc

  3. Foveal depression seen at 7 months

  4. By 4 months postpartum, the fovea is only one layer thick (cone nuclei)
• Optic Nerve Development

  1. Hollow optic stalk connects the third ventricle of the forebrain and the cavity of the optic vesicles

  2. As the choroidal fissure closes, a double layer of neuroectoderm is produced

  3. Ganglion cell axons from the retina pass along the inner layer of the stalk

  4. Eventually, the cavity between the inner and outer layers closes completely, forming the optic nerve
• Lens, Lids, Conjunctiva and Lacrimal Gland Development

  1. Lids, conjunctiva and the lacrimal gland begin developing around day 42 from surface ectoderm which folds on itself

  2. Ciliary muscle develops from migrating neural crest cells (NCCs)

  3. Extraocular muscles develop between days 28 and 70 from mesoderm

  4. Nasolacrimal system develops from NCCs, cannulation at day 120
• Maturing Eye


  1. Primary vascular vitreous starts to develop as soon as choroidal fissure closes

  2. Replaced by secondary avascular vitreous as hyalocytes produce hyaluronic acid (mesodermal origin) and vascular vitreous regresses (day 210)

  3. Retina continues to mature until term (day 270)
• Neuroectroderm Derivatives


  • Retina
  • Optic Nerves
  • Epithelium of the iris
  • Epithelium of ciliary body
  • Iris smooth muscle (sphincter and dilator pupillae)
• Surface Ectoderm Derivatives


  • Lens
  • Epithelium of cornea
  • Epithelium of conjunctiva
  • Epithelium of skin of eyelids
  • Glands of eyelid, lacrimal gland
• Mesoderm Derivatives


  • Extraocular muscles, orbicularis oculi and levator palpebrae superioris
  • Endothelium of the ocular blood vessels
  • Sclera (temporal portion) and Schlemm's canal
  • Vitreous (secondary, from hyalocytes)
• Neural Crest Cell Derivatives

  • Corneal stroma and endothelium
  • Sclera
  • Trabecular meshwork
  • Ciliary muscles
  • Melanocytes
  • Schwann cells
  • Meningeal sheath of optic nerve
  • Vitreous (primary)
• What happens after birth?

  1. Eyeball grows rapidly, initially relatively short (myopic or hypermetropic?)

  2. With rapid eyeball growth, the refractive error is corrected

  3. The cornea reaches adult size at 2 years old

  4. Lens grows rapidly and continues growing throughout adult life

  5. Pigmentation of the iris stroma occurs in the first few years

  6. Embryonic membranes in nasolacrimal system open at birth/shortly after which allows tears to begin to flow

  7. Retinal ganglion cells overlying fovea migrate allowing for improved VA
• Mittendorf dot


  A small white spot on the posterior aspect of the lens in the eye, representing the point where the hyaloid artery regresses during fetal development. Normal finding present in 1-3% of the population.
• Bergmeister papilla


  A remnant of the hyaloid artery that persists at the optic nerve head, appearing as a white, linear structure extending from the optic nerve head towards the posterior pole of the eye. Normal finding present in 1-2% of the population.
• Coloboma


  A type of birth defect that affects the eye, causing a gap or split in one of the structures of the eye