7.1 - Development of Eye and Ear

Question 1

Describe the development of the inner ear

Answer 1

1. Starts as otic placodes on back of head
2. Thicken and invaginate. Sinks below surface
3. Pinches off to form otic vesicle. Surface ectoderm closes over
4. Saccule forms cochlea. Utricle forms semicircular canals

Question 2

Describe the development of the middle ear

Answer 2

Tympanic cavity and auditory tube dervied from 1st Pharyngeal pouch (PP)

Ossicles formed from cartilage bar derivatives

1st PP expands distally to create the tympanic cavity.

Question 3

Describe the development of the external ear

Answer 3

• EAM forms from 1st pharyngeal cleft
• Auricles develop from auricular hillocks
• External ears develop initially in neck and as mandible grows ears ascend to side of head.

Question 4

What are the 2 main mechanisms from which congenital deafness can arise?

Answer 4

Middle ear deafness - problem with 1st and 2nd PA

Inner ear deafness - Maldevelopment of organ of corti commonly due to teratogenic agents

Question 5

Describe the development of the eye

Answer 5

1. Starts as outpocketings of forebrain (optic vesicles) which grow out to contact the overlying ectoderm
2. Area of contact forms lens placode which begins to thicken and invaginate and then pinch off and sink into optic vesicle.
3. Optic vesicle then stretches out to grasp lens placode for invagination, making a long slite running down the stalk known as the choroid fissure
4. Fissure closes around hyloid artery. Hyloid degenerates distally and becomes central artery
5. Rim of optic vesicle differentiates to form ciliary body musculature
6. Preoptic myotomes in eye form extraocular muscles
7. Optic cup forms from the optic vesicle and gives rise to retina, iris, and ciliary body
8. Optic stalk degenerates to form optic nerve
9. Intraretinal space develops as retina develops from 2 separate layers. Space is obliterated as layers fuse.

Question 6

How does a coloboma occur? What is a coloboma?

Answer 6

Coloboma - Hole in one of the structures in the eye

Occurs when the choroid fissure fails to close around the hyloid artery

Question 7

How and why does retinal detachment occur?

Answer 7

Trauma can open up the 2 fused layers of the retina, resulting in an opening of the intraretinal space.

Question 8

Where does the development of the eyes begin on the face? Where does it go?

Answer 8

Starts at side of head and as facial prominences grow the eyes move to the front of the face.

Question 9

How do congenital cataracts occur?

Answer 9

Form as a result of exposure to teratogen.