JOSE B IGLESIAS S.A.C.I.F

o Central a and v of retina 1st

o Central a of retina runs through the substance of the distal pt of the optic nerve lie in the choriodal fissure, but then buried in optic nerve o Initially lens is covered by vascular capsule

i. Hyaloids a Æ supp post pt of capsule, cont’n of central a, passes through vitreous 1. Hyaloids and vitreous disappear, but hyaloids canal persist

ii. Ant pt of capsule comes to be lined post by the iridial pt and forms iris

o Iridopupillary membrane Æ pupil closed by a pt of vascular tissue, disappears bf birth

Lens Surface ectoderm

Part Derived from

Retina Neuroectoderm (optic cup)

Vitreous Mesoderm

Choroid Mesoderm (infiltrated by neural crest cells)

Ciliary body Mesoderm

Ciliary muscles Mesenchymal cells covering the developing ciliary body (neural crest)

Iris Mesoderm

Muscles of iris Neuroectoderm (from optic cup)

Sclera Mesoderm (infiltrated by neural crest cells)

Cornea Surf epi by ecto, substantia propria and inner epi by neural crest

Conjunctiva Surface epithelium

Blood vessels Mesoderm

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x Eyelids Æ replication of surf ecto above and below the cornea Accessory Structures of Eyeball

o Ecto folds contain meso that give rise to muscle and to the tarsal plates

o Conjunctival sac Æ enlargement of folds where margins fuse together for a space x Lacrimal gland Æ formed from buds that arise from upper angle of conjunctival sac x Lacrimal sac and nasolacrimal duct Æ from ectoderm of naso-optic furrow

o Furrow lies along line of junction of maxillary process and lateral nasal process o Extends from medial angle of eye and region of the developing mouth

o Lacrimal sac Æ upp pt of cord that is formed from furrow being buried in ecto o Nasolacrimal duct Æ is lower part of cord, has secondary connection to nasal cavity o Lacrimal canaliculi Æ canalization of ecto buds that arise from the margin of ea eyelid

ƒ Near its medial end and grow to the lacrimal sac x Anophthalmos Æ eyeball fails to develop

x Microphthalmos Æ eyeball remains small x Cyclopia Æ two eyes fuse together

x Synophthalmos Æ eyes fuse partially, form one midline organ x Optic vessel may not be invaginated by the lens Æ remains a cyst

x Coloboma Æ choroidal fissure does not obliterate Æ deficiencies in various layers of the eye o Iris, ciliary body and choroid

x Cornea may be absent, anomalies of size and shape, may show congenital opacities x Blue sclera Æ sclera is thin and the pigment of the choroid can be seen

x Iris may show anomalies of its histological structure

o Rarely the sphincter or dilator pupillae muscle may be absent o Pupil may be abnormal in position, size or shape

x Rarely the lens may be absent or be very small; May be abnormal in position or shape

o Cataract Æ congenital opacities of lens Æ due to parathyroid deficiency, avitaminosis or infection of German measles during early pregnancy

x Persistent papillary membrane Æ vascular capsule of the lens persist and occludes the pupil o Hyaloids artery, vascular capsule of lens, or their remnants can persist

x Albinism Æ various layers of the eye may show too little pigmentation o Layers of the eye could also show too much pigmentation x Retina may show various congenital anomalies of its structure

o Could involve the macula Æ visual defects including colour blindness

Eyelids and Related Structures

Anomalies of Accessory Structures of Eye

x Eyelids rarely absent Æ no conjunctival sac Æ conjunctiva and cornea are replaced w/ skin x Coloboma of eyelid Æ part of the eyelid may be missing

o Underdevelopment of the tarsus or of the Meibomian glands

x Palpebral fissue may be abnormally wide or narrow Æ abnormal orientation and shape o Two lids may be completely or partially fused

x Epicanthus Æ abnormal fold of skin in relation to the lids Æ normal in some races x Entropion Æ lid margins are turned inwards

x Ectropion Æ lid margins are turned outwards (Rarely the whole lid may be inverted) x Ptosis Æ lavatory palpebrae superioris may fail to develop Æ drooping of lids x Eyelashes and eyebrows may be missing or duplicated

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Anomalies of the Lacrimal Apparatus

x Lacrimal gland may be absent or non-functional (may be ectopic) x Lacrimal passage may be absent in whole or part or atresia of some part

x Lacrimal duct could be open furrow on face Æ non-obliteration of the naso-optic furrow x Supernumerary puncta or canaliculi

x Otic placode Æ thickening of surf ecto overlying the developing hindbrain Æ memb labyrinth Internal Ear

x Otic pit Æ otic placode become depressed

x Otic vesicle Æ otic pit become rounded and seperates from surface ectoderm x Membranous labyrinth Æ differential growth of various pt of otic vesicle wall

o Give rise to specialized sensory end organs of hearing and of equilibrium ƒ Cristae of semicircular ducts

ƒ Maculae of utricle and saccule ƒ Organ of Corti of cochlea

o Innervated by peripheral processes of the cells of the vestibulocochlear ganglion ƒ Derived form the neural crest Æ cells remain bipolar throughout life x Bony labyrinth Æ formed from mesenchyme surrounding membranous labyrinth x Otic capsule Æ mesenchyme becomes condensed Æ converted into cartilage x Loose periotic tissue bt cartilage and membranous labyrinth

o Spaces of bony labyrinth created by disappearance of periotic tissue x Endolymph Æ fluid that fills the membranous labyrinth

x Perilymph Æ fluid that fills the periotic spaces

x Vestibule Æ space where periotic tissue disappears around utricle and saccule

x Semicircular canals Æ space where periotic tissue disappears around semicircular ducts x Two spaces are formed on either side of the cochlear duct

o Scala tympani Æ grows towards tympanic cavity from which it is separated by a membr o Scala vestibuli Æ communicates with the vestibule

x The cartilaginous labyrinth becomes ossified to form the bony labyrinth

x Tubo-tympanic recess Æ epithelia lining the middle ear and pharyngo-tympanic tube is derived Middle Ear

o Develops from the dorsal pt of 1st pharyngeal pouch and contribution from 2nd

x Tympanic antrum and mastoid air cells are formed from extensions from middle ear pouch x Malleus and incus Æ derived from dorsal end of Meckel`s cartilage

x Stapes Æ derived from dorsal end of cartilage from 2nd

x Ossicles are 1st pharyngeal arch

o Invaginate mucous mebrn which covers them throughout life outside the mucous mbrn of developing middle ear o Fully ossify in the 4th month of intrauterine life Æ 1st

x Tensor tympani Æ derived from meso of 1st _{pharyngeal arch and stapedius from 2} bones in the body to ossify nd _arch

x External acoustic meatus Æ derived from dorsal pt of 1 External Ear

st

o Deeper pt formed from proliferation of lining epi which grows toward middle ear ecto cleft

o Meatal plug Æ when proliferation is solid Æ later canalized

x Pinna (auricle) Æ formed from 6 meso thickening called tubercles or hillocks

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x Mandibular arch forms only the tragus and sm area around it, rest formed from hyoid arch o Consistent w/ the fact that auricular muscles are supplied by facial nerve

x Formed from apposition of the tube-tympanic recess and 1 Tympanic Membrane

st

o Forming the inner (endodermal) and outer (ectodermal) epithelia linings of membrane ecto cleft

o Intervening mesoderm forms the CT basis x Handle of malleus grows into CT from above

x Chorda tympani nerve 1st _{outside membrane, but later comes to lie w/in bc of upward ext}

x Development of auricle may get arrested at any stage Anomalies of the Auricle

o Result in being totally or partially absent, isolated nodules, or be very small or large x Migration from its primitive caudo-ventral position may remain incomplete

o Migration occurs bc of growth of maxillary and mandibular processes

o Ex association of caudo-ventral displacement of auricle w/ mandibulofacial dystosis

x Stenosis or atresia of meatus over its whole length or over part of it Anomalies of the External Auditory Meatus

o Lumen may be closed by fibrous tissue, by cartilage, or by bone

x Norm curvature of meatus may be accentuated Æ tympanic membr cannot be seen from outside x Ossicles may be malformed, may show abnormal fusion to one another or to wall of middle ear Anomalies of the Middle Ear

o Stapes may be fused to the margins of the fenestra vestibule x Facial nerve may bulge into middle ear and follow an abnormal course x Stapedial artery that disappears may persist

x Various pt of the membranous labyrinth may remain underdeveloped Anomalies of the Internal Ear

o Some cases cochlea alone is affected

o These anomalies lead to congenital deafness Timetable of Events

Eye

Age Developmental Events

22nd 4

day Appearance of optic sulcus (over the neural plate)

th

5

week Optic vesicle comes in contact w/ surface ectoderm Lens placode is forming

th

6

week Eye primordium is completely surrounded by loose mesenchyme

th

7

week Choriod fissure is formed; Lens vesicle is seen

th

The eyeball is most susceptible to teratogens during the 4 week A solid lens is formed

th

to 8th week, and can get affected till the end of pregnancy.

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Ear

Age Developmental Events

22nd 5

day Otic placode is seen

th

6

week Auricle starts forming

th

8

week The cochlea and semicircular canals starts forming

th

10

week The cochlea and semicircular canal assume their definitive external form

th

7

week Scala vestibule and scala tympani appear

th

The ear is most sensitive to teratogens during the 4

month External acoustic meatus gets canalized

th

to 9th weeks, and can be affected up to the 12th week.