Vision - Cornea Development

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Introduction

These notes introduce the development of the cornea of the eye. The adult cornea has three layers: an outer epithelium layer, a middle stromal layer of collagen-rich extracellular matrix between keratocytes and an inner layer of endothelial cells.


Vision Links: vision | lens | retina | placode | extraocular muscle | cornea | eyelid | lacrima gland | vision abnormalities | Student project 1 | Student project 2 | Category:Vision | sensory
Historic Embryology - Vision 
Historic Embryology: 1906 Eye Embryology | 1907 Development Atlas | 1912 Eye Development | 1912 Nasolacrimal Duct | 1917 Extraocular Muscle | 1918 Grays Anatomy | 1921 Eye Development | 1922 Optic Primordia | 1925 Eyeball and optic nerve | 1925 Iris | 1927 Oculomotor | 1928 Human Retina | 1928 Retina | 1928 Hyaloid Canal | Historic Disclaimer

Integumentary Development

Some Recent Findings

  • Bovine cornea extracellular matrix structure[1] "Electron microscopy and X-ray fibre diffraction were used to ascertain collagen fibril architecture. The bovine cornea was 1021±5.42μm thick at its outer periphery, defined as 9-12mm from the corneal centre, compared to 844±8.10μm at the centre. The outer periphery of the cornea was marginally, but not significantly, more hydrated than the centre (H=4.3 vs. H=3.7), and was more abundant in hydroxyproline (0.12 vs. 0.06mg/mg dry weight of cornea). DMMB assays indicated no change in the total amount of sulphated GAG across the cornea. Immunohistochemistry revealed the presence of both high- and low-sulphated epitopes of KS, as well as DS, throughout the cornea, and CS only in the peripheral cornea before the limbus. Quantification by ELISA, disclosed that although both high- and low-sulphated KS remained constant throughout stromal depth at different radial positions, high-sulphated epitopes remained constant from the corneal centre to outer-periphery, whereas low-sulphated epitopes increased significantly.
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<pubmed limit=5>Cornea Development</pubmed>

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<pubmed limit=5>Cornea Embryology</pubmed>

Frog Cornea

This developmental timeline is from a recent frog (Xenopus laevis) cornea study[2]

  • stage 25 - cornea starts from a simple embryonic epidermis overlying the developing optic vesicle.
  • stage 30 - detachment of the lens placode, cranial neural crest cells start to invade the space between the lens and the embryonic epidermis to construct the corneal endothelium.
  • stage 41 - a second wave of migratory cells containing presumptive keratocytes invades the matrix leading to the formation of inner cornea and outer cornea. A unique cell mass (stroma attracting center) connects the two layers like the center pole of a tent.
  • stage 48 - many secondary stromal keratocytes individually migrate to the center and form the stroma layer.
  • stage 60 - the stroma space is filled by collagen lamellae and keratocytes, and the stroma attracting center disappears. At early metamorphosis, the embryonic epithelium gradually changes to the adult corneal epithelium, which is covered by microvilli.
  • stage 62 - the embryonic epithelium thickens and cell death is observed in the epithelium, coinciding with eyelid opening.
  • After metamorphosis - cornea has attained the adult structure of three cellular layers, epithelium, stroma, and endothelium, and between the cellular layers lie two acellular layers (Bowman's layer and Descemet's membrane)


Links: Frog Development

Cornea Epithelia

Corneal Epithelial Cells cartoon

Corneal epithelial cells cartoon<pubmed>19668514</pubmed>

The cornea ocular surface is composed of three epithela, conjunctival, limbal and corneal.
  • Limbal stem cells are located in the palisades of Vogt, the transitional zone between the cornea and the conjunctiva.
  • Limbal stem cells are close to blood vessels.
  • They generate transient amplifying cells that terminally differentiate after a discrete number of cell divisions to corneal epithelial cells and undergo both centripetal migration and vertical migration.

Carnegie Stages - Eye

The following data is from a study of human embryonic carnegie stages[3] and other sources.

  • Stage 10 - optic primordia appear.
  • Stage 11 - right and left optic primordia meet at the optic chiasma forming a U-shaped rim.
  • Stage 12 - optic neural crest reaches its maximum extent and the optic vesicle becomes covered by a complete sheath,
  • Stage 13 - By the end of the fourth week the optic vesicle lies close to the surface ectoderm. Optic evagination differentiation allows identification of optic part of retina, future pigmented layer of retina, and optic stalk. The surface ectoderm overlying the optic vesicle, in response to this contact, has thickened to form the lense placode.
  • Stage 14 - (about 32 days) the lens placode is indented by the lens pit, cup-shaped and still communicates with the surface by a narrowing pore.
  • Stage 15 - (about 33 days) the lens pit is closed. The lens vesicle and optic cup lie close to the surface ectoderm and appear to press against the surface.
  • Stage 16 - (37 days) Growth of the lens body results in a D-shaped lens cavity. Perilental blood vessels (tunica vasculosa lentis) are visible. Prior to the development of the eyelids, one small sulcus or groove forms above the eye (eyelid groove) and another below it.
  • Stages 17 - 19 - Retinal pigment is visible and the retinal fissure is largely closed. Eyelids grooves deepen, eyelid folds develop, first below, and then above, the eye.
  • Stages 18 - Mesenchyme invades the region between the lens epithelium and the surface ectoderm.
  • Stages 19 - 22 - the eyelid folds develop into the eyelids and cover more of the eye as the palpebral fissure takes shape. The upper and the lower eyelids meet at the outer canthus in Stage 19.
  • Stage 20 - The lens cavity is lost and a lens suture begins to form. The inner canthus is established.
  • Stage 23 - The retina comprises the pigmented layer, external limiting membrane, proliferative zone, external neuroblastic layer, transient fiber layer, internal neuroblastic layer, nerve fiber layer, and internal limiting membrane. Eyelids closure is complete (Note - shown as still open in the Kyoto embryo).


Additional Images

Historic Images

References

  1. <pubmed>25019467</pubmed>
  2. <pubmed>23896054</pubmed>| Exp Eye Res.
  3. <pubmed>7364662</pubmed>


Reviews

<pubmed></pubmed> <pubmed>23819758</pubmed> <pubmed>20599432</pubmed>| PMC3726544 <pubmed>19343693</pubmed>


The International Journal of Developmental Biology Vol. 48 Nos. 8/9 (2004) Eye Development

Articles

<pubmed></pubmed> <pubmed></pubmed> <pubmed>13429485</pubmed>| PMC1358888


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Cite this page: Hill, M.A. (2024, March 28) Embryology Vision - Cornea Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Vision_-_Cornea_Development

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