Chapter 9

Question 1

Failure of the choroid fissure to close results
in
(A) congenital detached retina
(B) congenital aniridia
(C) congenital aphakia
(D) coloboma iridis
(E) microphthalmos

Answer 1

D. 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.

Question 2

The epithelium of the ciliary body
derived from
(A) ectoderm
(B) mesoderm
(C) endoderm
(D) neuroecloderm
(E) neural crest cells

Answer 2

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

Question 3

Hyperoxygenation of premature infants may result in
(A) congenital glaucoma
(B) microphthalmia
(C) coloboma
(D) retrolental fibroplasia
(E) persistent pupillary membrane

Answer 3

D. 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.

Question 4

The optic nerve is a tract of the diencephalon
that is not completely myelinated
until
(A) 5 years after birth
(B) 2 years after birth
(C) 1 year after birth
(D) 3 weeks after birth
(E) 3 months after birth

Answer 4

E. 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 CNS is accomplished by oligodendrocytes; oligodendrocytes are not found in the retina.

Question 5

Aqueous humor is produced by the
(A) choroid plexus
(B) trahecular meshwork
(C) ciliary processes
(D) vitreous body
(E) lens vesicle

Answer 5

C. 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.