Table 1.3 Embryonic origins of ocular tissues.
| Neural ectoderm | Neural crest |
|---|---|
| Neural retina | Stroma of iris, ciliary body, choroid, and sclera |
| RPE | Ciliary muscles |
| Posterior iris epithelium | Corneal stroma and endothelium |
| Pupillary sphincter and dilator muscle (except in avian species) | Perivascular connective tissue and smooth muscle cells |
| Striated muscles of iris (avian species only) | |
| Bilayered ciliary epithelium | Meninges of optic nerve |
| Orbital cartilage and bone | |
| Connective tissue of the extrinsic ocular muscles | |
| Endothelium of trabecular meshwork | |
| Surface ectoderm | Mesoderm |
| Lens | Extraocular myoblasts |
| Corneal and conjunctival epithelium | Vascular endothelium |
| Lacrimal gland | Schlemm's canal (human) |
| Posterior sclera (?) |
It is important to note that mesenchyme is a general term for any embryonic connective tissue. Mesenchymal cells generally appear stellate and are actively migrating populations with extensive extracellular space. In contrast, the term mesoderm refers specifically to the middle embryonic germ layer. In the eye, mesoderm probably gives rise only to the striated myocytes of the extraocular muscles (EOMs) and vascular endothelium. Most of the craniofacial mesenchymal tissue comes from neural crest cell.
Formation of the Optic Vesicle and Optic Cup
The optic sulci are visible as paired evaginations of the forebrain neural ectoderm on day 13 of gestation in the dog (Figure 1.1). The transformation from optic sulcus to optic vesicle is considered to occur concurrent with the closure of the neural tube (day 15 in the dog).
Figure 1.1 Development of the optic sulci, which are the first sign of eye development. Optic sulci on the inside of the forebrain vesicles consisting of neural ectoderm (shaded cells). The optic
