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Neural Biology 1 > eye development 2 > Flashcards

eye development 2 Flashcards

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1
Q

How do you get your retina and your lens being derived from ectoderm?

A

retina is an out pouching of your brain

  • then go through some processes where it evaginates to form optic cup
  • then matures into future retina
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2
Q

What does the back region of the optic cup form?

A

RPE

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3
Q

What happens as the growing vesicle touches the surface ectoderm?

A
  • promotes surface ectoderm to start envaginating and that forms lens pit which then forms the lens vesicle then matures init lens , first posteriorly from primary lens fibres, growing to fill void in centre of lens vesicle, then when thats filled secondary lens fibres starts to elongate backwards from your anterior surface
  • thats fed by the vascular supply that comes through the choroidal fissure init the centre of optic cup.
  • that hyloid vasculature feeds developingoptic cup, also grows forward and forms a meshwork around the developing lens called the tunica vascularis lens
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4
Q

What happens in the later developers ?

A
  • start to get maturation of future vitreous chamber
  • Embryonic Weeks 6-8 & initial Fetal period, starting ~Week 12)
    1. Secondary Vitreous & Chambers
    2. Choriod, Sclera & Cornea
    3. Ciliary Body & Iris
    4. Tertiary Vitreous
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5
Q

How does these chambers form ?

A

-Involve multiple changes in the Mesenchyme/mesoderm inside & outside the developing Eye Cup:

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6
Q

What is the primary vitreous?

A

when we have optic cup being formed we have this region between our developing retina and lens vesicle filled with mesoderm
-which are fibroblast like cells which can convert into connective tissue cells in future and they secrete extracellular to help invagination of this optic cup - this the primary vitreous

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7
Q

How is a secondary vitreous formed?

A

the primary vitreous has to mature

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8
Q

What happens inside the developing cup ?

A

-Inside: appearance of Secondary (fluid) Vitreous & Chambers by ‘Vacuolization’ + additional vascular membranes form on anterior lens face (TVL) & between Chambers (pupillary membrane)

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9
Q

What happens outside the developing cup ?

A

-Outside: appearance of Choroid, Sclera & Cornea by process of ‘Condensation’ + Angiogenesis & Eyelids through folding

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10
Q

What is happening in the vitreous chamber INSIDE ?

A

blood vessels start to secrete fluid into the space (region) and the extracellular matrix is brown down and absobred by mesoderm cells.

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11
Q

What is formed INSIDE developing eye cup ?

A

2 chambers forming infront of the developing lens which are sepearetd by a capillary membrane

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12
Q

What happens OUTSIDE the developing cup ?

A
  • formation of outercoats
    -formed through 2 processes
    condensation and angiogenesis
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13
Q

What happens in condensation OUTSIDE the cup?

A

where mesodermal cells start to proliferate and condense down and create brown substance

  • form a very dense material surrounding the developing optic cup which make form chord, sclera and cornea
  • the structure is growing hence limited amount of diffusion of nutrients and oxygen unlike at the primary vitreous where a blood supply wasn’t needed and would diffuse through tissues 1/2mm
  • as structure gets bigger , now needs a blood supply
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14
Q

What happens in angiogenesis OUTSIDE the cup ?

A
  • as there is limited amount of nutrients and oxygen supply need a blood supply
  • these whole tissues have to be vasulcarised by the princess of angiogenesis
  • this allows developing tissues to grow larger as they have a regular nutrient supply
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15
Q

What else happens OUTSIDE the developing cup ?

A
  • eyelids being developed
  • through folding of mesoderm outside the developing cup
  • also the surface ectoderm also has to be folding along this
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16
Q

What are myoblasts ?

A
  • precursor cells for muscles
  • subset of those developing mesodermal cell
  • aggregate on condensing sclera & in the eyelids to form the Extraocular Muscles.
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17
Q

What are Osteoblasts?

A
  • bone precursor cells

- aggregate in membranes around these to form the Orbital bones

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18
Q

What do the cells of the primary vitreous start the process of ?

A

Vacuolisation

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19
Q

What happens inside optic cup?

A

Vacuolisation

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20
Q

What is vascuolisation?

A

where those internal structures inside of your optic cup which become spaces which we have later in life
- need them to be fluid filled with very few cells

21
Q

What happens in vascuolisation?

A

1) Cells of Primary Vitreous create spaces by
absorbing fibres & secreting fluid into matrix

  • we have fibroblast cells in there start to break down the extracellular matrix and reabsorb it
  • at the same time your hyloid vasculature and posterior tunica vascularis lenses start to leak and secrete out into the vitreous space fluid.
  • as that occurs you also get fibroblasts secreting proteoglycans in this environment.
  • Retro-lental Space: creates Secondary Vitreous Body

(2) Mesenchymal Cells between Lens Vesicle &
Surface Ectoderm do likewise
-2 Spaces appear: Anterior & Posterior Chambers
-Divided by vascular/fibrous Pupillary Membrane
-Similar membrane on anterior face of lens, now surrounded by complete vascular capsule (TVL), supporting

22
Q

How do we create the secondary vitreous fluid ?

A
  • secrete fluid from hyloid vasculature to make it this chamber that is optically clear
  • need the pressure of this fluid build up to help force the optic cup to grow outwards
23
Q

What extends ?

A

ciliary retina to from ciliary body and grow along this pupillary membrane to form the iris and then ultimately will break down to form the pupil
-until that stage you maintain the pupillary membrane separating your anterior and posterior chamber.

24
Q

What happens outside the optic cup ?

A

condensation

-how your outer coat and choroid is formed

25
Q

What happens in condensation ?

A
  1. Surrounding Connective Tissue cells produce
    more fibres & reduce extracellular matrix
  • Neurectomesenchyme next to the Optic Cup:
    • Forms the Middle layer (Choroid layer), invaded posteriorly & anteriorly by blood vessels to form choroid
  • it is adjacent to your developing RPE on the outside- this is going to go on and form the choroid.
  1. Mesenchyme/ mesodermal cells further from the Optic Cup:
    - Forms the Outer Layer; Cornea (stroma) & Sclera
    + Posteriorly on Sclera: Extraocular Muscles attach
    + Anteriorly: folding of upper & lower Eyelids
26
Q

How do we form the Neurectomesenchyme?

A
  1. A Mixture of Mesenchyme (Mesodermal connective
    tissue cells fibres & matrix) + Neural Crest cells
    -Evagination of Optic Vesicle from CNS (Neural Tube) into surrounding mesenchyme
    -Drags along with it cells that have detached from the adjoining Neural Crest
NB: Neural Crest cells also give rise to all the melanocytes of
the eye (in the iris & choroid) & of the skin
27
Q

When you have the ectoderm ?

A
  • motor chord which directs to centre region on ectoderm to develop for neural plate which made neural tube
  • the peripheral tissue become surface ectoderm and green region become neural crest cells - are neuroectoderm- break off and migrate to mesoderm
  • some make PNS or draw into the ocular structure being developed- neural crest cells mix with mesoderm to form neuronectomesenchyme to form choroid
28
Q

How are melanocytes made?

A

–melanocytes directly made form neural crest cells

29
Q

What is the next period ?

A

the late arrivals

-now out of the embryonic peirod

30
Q

What happens in the late arrival ?

A

ciliary body starts to form , week 12 (1 month into fetal life)

31
Q

How is the iris in pupillary membrane made ?

A

-Iris, in Pupillary Membrane
Stroma & Sphincter smooth muscle:
-come from Neurectomesenchyme

-Dilator muscle ( not really a muscle): = known as myo-epithelium (fibrillin): from the Neurectoderm of the ciliary retina = Neural-tube-derived (from the brain!)

32
Q

How is the Ciliary Body, posterior to lens formed ?

A

Ciliary Body, posterior to lens
Smooth Muscle: from Neurectomesenchyme
Ciliary Processes & Zonule: also from Neurectoderm of ciliary retina = Neural-tube-derived (from the brain!)
-suspensosory ligaments that hold lens in place are myosin epithelial ells from the same lineage from your brain tissue

33
Q

What does the RPE do?

A

continuous processes which form the ciliary processes for ciliary body for iris

34
Q

How is the dilator muscle formed ?

A

some of these epithelial cells bud off and invade mesoderm and start to form the dialator muscle

35
Q

What structures of the eye come from the surface ectoderm ?

A

lens

  • cornela epithelium
  • conjunctival epithelium
  • cilia
  • epithelium, tarsal glands
  • epithelium zeis aan moll glands
  • epithelium, lacrimal and accessory lacrimal glands
  • epithelium, lacrimal passages
36
Q

What structures of the eye come from the mesoderm ?

A
  • conreal stroma
  • corneal endothelium (mesoethilum)
  • and descements membrane
  • blood vessels
  • sclera
  • choroid
  • conjunctival stroma
  • episclera
  • tenon capsule
  • iris stroma
  • extrisinic eye muscles
  • ciliary muscle
  • bones of orbit
  • vitreous
37
Q

What comes from the eye from neural ectoderm ?

A
  • sensory retina , RPE
  • ciliary body epithelium- pigmented and non pigmented
  • pigmented epithelium of iris
  • sphincter pupillae muscle, dilator pupillae muscle
  • neurologic and neural portions of optic nerve
  • melanocytes
  • ciliary zonule
  • contribution to ciliary and constrictor muscles
38
Q

What are the Abnormal Eye Development:

When Things Go Wrong
?

A

(1) Failures of Early Embryonic Development
Severe malformations, some preclude extra-uterine life
Anophthalmia ( no eyes) , cyclopia (only have 1. eye), persistent primary vitreous (dont develop fluid filled cavity - dont get vascularisation in eye - leading to micoropthalmia )
(2) Failures of Later Embryonic &/or Fetal Development
Surmountable problems
Coloboma iridis (inability of choroidal fissure to close properly- normally closes as a zip- so if can’t then will cause problems- esp for retina- if close half way- later on in development will be affected - so get keyhole iris ), congenital capsular cataract

39
Q

WhatoOther Events in Fetal Life ?

A

-3rd & 4th Months
Pupillary Membrane degenerates (as Iris within it develops), so that the Pupil aperture is patent (open)
Tunica Vascularis Lentis atrophies, as Ciliary Processes develop & supply nutrients to lens via Aqueous Humor production

40
Q

What happens 5th month onwards ?

A

-5th Month onwards
Blood flow ceases in distal Hyaloid vessels & they degenerate: but leave a trace (canal in Tertiary Vitreous)- lose hyloid vasculature you generate tertiary vitreous

41
Q

what happens at 7th and 8th month?

A

7th & 8th Months
Eyelid suture unfuses, so that palpebral aperture is patent
Retina: neurons differentiated & axons connected to brain
The Eye is ready for rudimentary Vision
-neurons are fully differentiated - synapse now form proper synaptic connections
-

42
Q

a

A

a

43
Q

What are some other development failures ?

A
  1. Persistent Hyperplastic Primary Vitreous
    Hyaloid Vessels & TVL fail to degenerate, vitreous remains fibrous/vascular, eye fails to grow (micro-ophthalmia)
  2. Congenital Capsular Cataract
    TVL fails to degenerate, fibrous/vascular lens capsule: occludes light entry, Vision severely reduced
  3. Coloboma iridis
    Choroidal/Optic Fissure fails to close, effects variable
    • Early: retina & optic nerve (with serous choroidopathy)
    • Late: iris only affected (asymptomatic)
44
Q

What happens in congenital capsular Cataract ?

A
  • 2 Main Types (~1:3000 births; 50:50, nuclear: capsular)
  • Nuclear: affects lens cells, proteins prematurely sclerotic
  • Usually both eyes affected & due to teratogen (common= maternal measles or viruses)
  • Capsular: fibro-vascular tunic retained (sporadic)
  • Often unilateral & a cause of deprivation amblyopia
45
Q

What is not likely to happen ?

A

not very likely to have eye abnormalities

46
Q

What is Coloboma iridis?

A

Mild or asymptomatic type

  • Choroid fissure at ventral pole of developing anterior rim fails to close- fail to close early in development - so retina and optic nerve affected- can lead to a bad condition.
  • ‘Key-hole’ pupil, with discontinuity located at ventral pole of the iris
  • Severe type, discontinuity extends posteriorly down the retina & optic nerve……
47
Q

What is synophthalmia ?

A

cyclopia

  • caused by when you have you brain development - you develop 2 lobes of your Brian - left and right- ion there is blockage of the signalling taking place that splits your body - both structures will grow but can’t differentiate where yo grow - eye vesicle will go together so will fuse together and form
  • caused by environmental factors sometimes genetic
48
Q

What is anophthalmia?

A
  • no eyes
  • ## no forming of neruoectoderm to form optic cups
49
Q

To which of the following developing ocular cells or
tissues do embryonic neural tube cells NOT contribute?

  1. Dilator muscle of the iris
  2. Melanocytes of the choroid
  3. Retinal pigment epithelium
  4. Suspensory ligament of the lens
A

Melanocytes of the choroid

Neural Biology 1 (58 decks)

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