Histology II: Embryology of Eye and Ear

The developing eye appears on … of embryonic development as a shallow groove in the sides of the forebrain, they are a direct exension of the brain

day 22

…: an invagination of the forebrain from which the neural part of the eye will form

Optic vesicle

The optic vesicle is visible by …

week 4

…: the connection of the optic vesicle to the diencephalon

optic stalk

…: induced to form from the surface ectoderm by the optic vesicle

lens placode

Both the lens placode and the optic besicle …

invaginate

…: forms from the invagination of the optic vesicle, two-layered

optic cup

…: forms from the invagination of the optic stalk

choroid fissure

…: forms from the invagination of the lens placode

lens vesicle

…: grows through the choroid fissure to supply the lens

hyaloid artery

Derivatives of the optic cup: … (4)

Pigment layer of retina, neural layer of retina, intraretinal space, future pupil

Formation of the eye proper: the optic stalk differentiates into the …

optic nerve

Formation of the eye proper: elongation and extension of the lens posterior cells generate … that will eventually form the lens

lens fibers

Formation of the eye proper: the … start to form from ectoderm and mesoderm above and below the eye

eyelids

Formation of the eye proper: the … (2) develop from both the outer (pigmented) and inner (neural) layers of the optic cup

iris, ciliary body

Formation of the eye proper: the … (2) develop from mesoderm surrounding the optic cup

sclera, choroid

The cornea develops from: … (2)

surface ectoderm, mesoderm

…: an area of missing tissue in the eye (iris, retina, choroid), congenital, due to failure of the choroid fissure to completely fuse

coloboma

…: the most common but defects could extend into other parts of the eye

Coloboma iridis

Coloboma iridis can cause: … (3)

light sensitivity, low vision, nystagmus

Mutations in … have been linked to optic nerve colobomas

PAX2

…: the complete or partial absence of the iris, congenital, bilateral, isolated or syndromic

Aniridia

Aniridia can cause: … (2)

blurry vision, photophobia

Aniridia is caused by mutations in …

PAX6

…: the lens is cloudy at birth, protein build-up, genetically determined

congenital cataracts

Congenital cataracts can be due to: … (6)

chickenpox, measles, rubella, CMV, toxoplasmosis, syphilis

…(2): a spectrum of diseases in which the eyes are partially or completely fused

cyclopia, synopthalmia

Cyclopia is due to: … (2)

loss of midline tissue, underdevelopment of forebrain and frontonasal process

Cyclopia is associated with …

holoprosencephaly

Cyclopia can be genetic and is seen with mutations in …

SHH

…: can be associate with syclopia, altered cholesterol metabolism

smith-lemli-optiz syndrome

Cyclopia is caused by: … (3)

alcohol exposure during pregnancy, maternal diabetes, abnormal cholesterol metabolism

Inner ear development begins with thickening of the …

surface ectoderm

…: thickening of the surface ectoderm

otic placodes

…: formed by the invagination of the otic placodes

otic vesicle

…: originated from neurons of he otic vesicle and neural crest cells

statoacoustic ganglion

The otic vesicle will give rise to all …

inner ear structures

The tympanic cavity and auditory tube derive from the endoderm of …

first pharyngeal pouch

Derive from the first pharyngeal pouch of the endoderm: … (2)

tympanic cavity, auditory tube

…: embryonic structures that will give rise to structures of the head and neck

pharyngeal arches

Ear ossicles dervie from …

neural crest cells

Derive from the neural crest cells in the first pharyngeal arch: … (2)

malleus, incus

Derive from the neural crest cells and mesoderm in the second pharyngeal arch: …

stapes

The …. derives from the ectoderm of the first pharyngeal cleft

external auditory meatus

The … derives from ectoderm, endoderm and mesoderm

eardrum

the auricle develops from …

auricular hillocks of 1-2 pharyngeal arches

…: neural crest proliferations

auricular hillocks

The auricle initially positioned in the … but moves up as the mandible grows

lower neck region

Congenital external ear deformities: … (5)

anotia, skin tags (extra hillocks), pits (lack of hillock fusion), positioning, deformities from deficient hillock formation

… may occur from the ear down towards the neck

skin tags

…: a defect in the sensory (hair cells) or neural (auditory nerve ganglia) components of the inner ear, 90% of hearing loss

Sensorineural hearing loss

Sensorineural hearing loss is due to defects in: … (2)

cochlea (associated structures), vestibulocochlear nerve (VIII)

Congenital hearing loss can be due to: … (5)

prematurity, maternal diabetes, lack of oxygen, genetics, infectious disease during pregnancy

…: a structural defect in the external or middle ear, defect in transfering the sound waves (autosomal recessive X-linked)

Conductive hearing loss

Congenital hearing loss can be syndromic: … (2)

treachers Collins syndrome, down syndrome

Stapes is most common ear ossicle involved in conductive hearing loss due to its … origin

dual mesodermal and neural crest cell