Eye Embryology Questions

Failure of the choroid (optic) fissure to close results in a cleft of the iris—a coloboma iridis. This defect may extend into the ciliary body, choroid, optic nerve, or retina. Congenital
aphakia—absence of the lens—may result from defective development of the lens placode.

The optic cup and its derivatives—the retina and optic nerve—develop from
the diencephalon

Retrolental fibroplasia results from hyperoxygenation of premature infants. In premature
infants, high oxygen concentration results in vaso-obliteration of the terminal arterioles, leading
to hemorrhage and infarction of the retina. This phenomenon is peculiar to the incompletely
vascularized peripheral retina.

Aqueous humor enters the venous circulation via the canal of Schlemm. Blockage of this
canal results in increased intraocular pressure (glaucoma).

The lens forms from the lens placode that is induced by the optic cup

Aqueous humor is produced by the ciliary processes of the ciliary body. It flows from the
posterior chamber, through the pupil, into the anterior chamber, and finally to the canal of
Schlemm, which empties into the extraocular veins

The site of retinal detachment is between the pigment epithelial layer and the layer of outer
segments of rods and cones; this corresponds to the intraretinal space between the inner and
outer layers of the optic cup. Retinal detachment occurs when fluid from the vitreous compartment passes through a retinal hole and separates the pigment epithelial layer from the layer of
outer segments of rods and cones.

The hyaloid canal (Cloquet’s canal) is found in the vitreous body. In early development, a
hyaloid artery passes through the vitreous body to perfuse the developing lens; in the late fetal
period, this artery is obliterated to form the hyaloid canal

The axons of the optic nerve are not completely myelinated until 3 months after birth.
Myelinated axons are normally not found in the retina. The optic nerve is not a true peripheral nerve but a tract of the diencephalon; when severed, the optic nerve does not regenerate. Myelination in the central nervous system (CNS) is accomplished by oligodendrocytes;
oligodendrocytes are not found in the retina.

The ciliary body is derived from the anterior two layers of the optic cup (neuroectoderm),
which form the epithelium, and from an anterior extension of the choroid (mesoderm).