Test 108   (Ocular embryology)

1. The following are true: 

a. optic pits first appear on day 13 of gestation

b. evagination of the optic vesicle occurs on day 25 of 
    gestation

c. closure of optic fissure occurs on day 33 of gestation

d. closure of optic fissure occurs anteriorly and extends
    backwards

e. failure of optic fissure closure results in iris and lid 
    coloboma

Answera.F  b.T  c.T  d.F  e.F
Optic pits first appear on day 23 of gestation. Closure of optic fissure begins midway and extends anteriorly and posteriorly. Failure of optic fissure results in iris and choroidal coloboma but not lid coloboma.
 

2. The pairings of the following are correct:

a. lacrimal gland - surface ectoderm

b. Schlemm's canal - mesoderm

c. choroid - mesoderm

d. retinal pigment epithelium - neural ectoderm

e. iris stroma -neural crest

Answera.T   b.T   c.F   d.T  e.T
The choroid is derived from the neural crest.

 
3. The following results from remnants of the hyaloid vasculature 
    system:

a. Peter's anomaly

b. Bergmeister's papilla

c. persistent pupillary membrane

d. Mittendorf's dot

e. posterior lenticonus

Answera.F   b.T  c.T  d.T  e.F
Peter's anomaly results from anterior cleavage syndrome and gives rise to leukoma. Posterior lenticonus is a congenital abnormality of the lens unrelated to the hyaloid vasculature system.

4. With regard to myelination:

a. in the majority of people, optic nerve myelination 
    terminates at the lamina cribrosa

b. myelination of the retinal nerve fibres layer does not 
   affect the vision

c. optic nerve myelination begins at seventh month of 
    gestation

d. optic nerve myelination is completed just before birth
    in full term baby

e. optic nerve myelination begins at the occipital cortex
 

Answera.T  b.F  c.T  d.F  e.F
Optic nerve myelination begins at the optic chiasm. The myelination is completed one month after birth in full-term baby. Myelination of the nerve fibre layer if extensive can cause poor vision.

5. The following are true:

a. retinal vascularization begins at the 4th month of 
    gestation

b. the nasal peripheral retina is the last to vascularize

c. the main vitreous body is derived from the primary 
    vitreous

d. the hyaloid system is part of the secondary vitreous

e. the zonules are derived from the tertiary vitreous

Answera.T  b.F  c.F  d.F  e.T
The main vitreous body is derived from the secondary vitreous. The hyaloid system is part of the primary vitreous.

 
 

More MCQs