2020–2021 BCSC Basic and Clinical Science Course™
2 Fundamentals and Principles of Ophthalmology
Part II: Embryology
Chapter 4: Ocular Development
Eye Development
Cornea, Anterior Chamber, and Sclera
Cornea and anterior chamber
Surface ectoderm closes over the lens pit and gives rise to the corneal epithelium (see Fig 4-6D). This is followed by 3 successive waves of migration of neural crest–derived cells (Figs 4-15, 4-16; see also Fig 4-6E). The first wave of ectomesenchymal cells, passing between the surface ectoderm and the anterior lens vesicle, gives rise to the corneal endothelium. The second wave, consisting of cells of neural crest and mesodermal origin, contributes to the iris and part of the pupillary membrane. The third wave, consisting of ectomesenchymal cells, migrates into the space between the endothelium and the epithelium to give rise to the keratocytes of the corneal stroma. The corneal endothelial cells meet with developing iris, forming the angle recess. The trabecular meshwork and the Schlemm canal develop from mesenchymal cells posterior to the recess. The endothelial cells that line the canal and collector channels are derived from adjacent capillaries, which will eventually form the episcleral venous plexus. The resultant aqueous vein receives aqueous humor and delivers it to the venous circulation (see Chapter 2, Figs 2-17, 2-18). The trabecular beams undergo further maturation and stratification to form the layered trabecular meshwork. Alteration in this process has been implicated in the development of congenital glaucoma and anterior chamber dysgenesis. The scleral spur forms between the trabecular meshwork and the ciliary muscle as the anterior chamber angle develops (see Fig 4-13C, D).
Sclera
The sclera is formed from mesodermal (temporal sclera) and neural crest–derived ectomesenchymal elements. The sclera joins the developing cornea near the equator of the eye but continues to develop and expand to surround the developing optic cup. The scleral spur and Tenon capsule form later, at the time of extraocular muscle insertion.
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.