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Head and Neck Anatomy > Development of the Eye > Flashcards

Development of the Eye Flashcards

1
Q

Eyes are derived from which four sources?

A
  1. Surface ectoderm of the head
  2. Lateral neuroectodermal walls of the embryonic diencemphalon brain
  3. Mesenchyme (mesoderm) between the above two layers
  4. Neural crest cells
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2
Q

When does development of the eye begin?

A

4th week
- 22 days

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3
Q

Describe the development of the optic cup and lens vesicle?

A
  1. A pair of shallow grooves (optic grooves/sulcus) appear on the sides of the forebrain
  2. As neural tube fuse to form forebrain
    - Optic grooves evaginate to form optic vesicles (hollow diverticula) : induced by mesenchyme adjacent to the brain
    - Optic vesicle cavities becomes continuous with cavity of the forebrain
  3. As optic vesicles expand their connections constrict to form optic stalks
  4. As optic vesicles contact surface ectoderm It induces the surface ectoderm to thicken to form lens placodes
  5. Lens placodes later evaginates and sinks into surface ectoderm forming lens pits
  6. Edges of pits later fuse to form lens vesicle which later pinches off the surface ectoderm
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4
Q

Thickening of the surface ectoderm’s in contact with optic vesicles forms which structures?

A

Lens placodes

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5
Q

What are the layers of the optic cup?

A
  1. Inner layer - neuroepithelium
    “neural retina”
  2. Outer layer - retinal pigment
    Epithelium
  3. Between - Intraretinal space
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6
Q

What happens as the lens vesicle develops?

A
  1. Optic vesicles invaginate to form double layered optic cups
  2. Linear grooves (retinal fissures /optic fissures) develop on the ventral surface of the optic cups
    - passage of hyaloid artery & vein (branch of opthalmic artery/vein)
  3. As optic fissures fuse, they enclose these vessels within primordial optic
    nerve
  4. Vessels later become central artery/vein of the retina
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7
Q

Where does the central artery develop from?

A

Optic vesicles

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8
Q

Describe the hyaloid system?

A
  • As the optic vesicle develops there is incomplete folds in its inferior portion of cup and stalk called embryonic fissure
  • Embryonic fissure allows hyaloid system to be incorporated within the eye.
  • In 5th week Hyaloid artery enters the embryonic fissure of optic stalk
  • With the fusion of fissure the hyaloid system are enclosed within the eye
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9
Q

What is a Coloboma?

A
  • Failure to close choroidal/optic fissure
  • Key hole appearance in iris
  • Follow AD inheritance
  • Position: infero-nasal quadrant reflective of the location of the optic fissure during development
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10
Q

Describe the development of the retina?

A

Develops from walls of optic cup.
Outer thin layer forms the retina pigment epithelium
Inner thick layer forms neural retina
During embryonic /fetal periods the two layers are separated by intraretinal space
Later fuse loosely

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11
Q

The optic nerve is formed from?

A

Axons of ganglion cells
- myelination is incomplete at birth

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12
Q

The optic cup walls develop to form which structure?

A

Retina

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13
Q

What is congenital detachment of the retina?

A

When the outer and inner layers of the optic cup fail to fuse

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14
Q

Describe the development of the ciliary body?

A
  1. Pigmented portion of the ciliary epithelium
    - is derived from outer layer of optic cup.
    - Is continuous with retina pigmented epithelium
  2. Non-Pigmented portion of the ciliary epithelium
    - Is anterior prolongation of neural retina epithelium
  3. The ciliary muscle
    - develops from mesenchyme located at the edge of the optic cup
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15
Q

The mesenchyme located at the edge of the optic cup develops into?

A

Ciliary muscles

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16
Q

Describe the development of the iris?

A
  • Develops from the rim of the optic cup which grows inward
  • The two layers of the cup remain thin in this area
17
Q

What is iris epithelium?

A
  • Represents both layers of the optic cup
  • Is continuous with the double layered epithelium of the:
    • Ciliary body
    • Retina pigment epithelium and neural retina
18
Q

The dilator and sphincter pupillae muscles arise from?

A

Neuroectoderm

19
Q

The structure of the eye that develops from the inward growth at the rim of the optic disk is called?

A

Iris

20
Q

Describe the development of the lens?

A

Develops from lens vesicle
- a derivative of surface ectoderm

  1. Anterior wall composed of cuboidal epithelium forms the sub capsular lens epithelium
  2. The posterior wall - forms tall columnal cells that eventually lose their nuclei (called primary lens fibers)
21
Q

What is the rim of the lens called?

A

The rim of the lens is called the equatorial zone
- Cuboidal cells of the equatorial zone continuously elongate, lose nuclei and become secondary lens fibers

22
Q

The lens develops from?

A

Lens vesicle

23
Q

Describe the vasculature of the lens?

A

Developing lens is invested by a vascular mesenchymal layer (dense capillary network) called tunica vasculosa lentis
- Anterior part of this capsule forms the pupillary membrane

24
Q

What supplies the tunica vasculosa lentis?

A

The hyaloid artery
- When the hyaloid artery later degenerates in the fetal periods, tunica vasculosa lentis also degenerates leaving behind a hyaloid canal

25
Q

Mention the structure whose is as dense network of capillaries that provides nourishment to the lens during its initial development?

A

Tunica vasculosa lentis

26
Q

What is the tunica vasculosa lentis?

A
  • A vascular mesenchymal layer
  • Forms around the lens during its development
  • At 1st month of gestation, Hyaloid artery gives rise to small capillaries which forms the Posterior pupillary membrane, a network covering posterior surface of the lens capsule
  • Grows towards the equator of he lens
  • Fully developed at 9th week of gestation
27
Q

Describe the development of the aqueous chambers?

A
  1. Anterior chamber
    - Develops from cleft-like space that forms in the mesenchyme between developing lens and cornea.
  2. The posterior chamber
    - Develops from a space that forms in the mesenchyme posterior to the developing iris and anterior to the developing lens
28
Q

The cleft like space that forms the mesenchyme between developing lens and cornea is called?

A

Anterior chamber

29
Q

The space that forms in the mesenchyme posterior to the developing iris and anterior lens is called?

A

Posterior chamber

30
Q

Describe the development of the cornea?

A
  1. External corneal epithelium is derived from surface ectoderm
  2. CT or mesenchyme is derived from mesoderm
    - continuous with developing sclera
  3. Neural crest cells migrate to cornea and forms the corneal endothelium
31
Q

Which corneal layer develops from neuro crest cells?

A

Corneal endothelium

32
Q

Describe the development of the choroid and sclera?

A
  • develop from condensation of mesenchyme (neural crest origin) surrounding optic cup
  • At the rim of optic cup, the choroid becomes modified to form ciliary processes consisting of capillary blood vesses with CT
33
Q

Describe the development of the eyelids?

A

Develop in the six the week from:
1. neural crest cell mesenchyme
2. Two folds of skin that grow over cornea
• Adhere to each other in 10th week and re-open in the 26th-28th week
• Conjuctiva sac develops and lies anterior to the cornea

34
Q

Surface ectoderm differentiates into?

A
  1. Lens of the eye
  2. Cornea epithelium
35
Q

Name the 3 structures of the eye that develop from neuroectoderm?

A

• Differentiates into :
1. Retina
2. Posterior layers of the iris
3. Optic nerve

36
Q

Name the structures the mesenchyme (mesoderm) differentiates into?

A

• Differentiates into:
1. Fibrous coat of the eye
2. Vascular coat of the eye

37
Q

Name the 3 structures that develop from neurons crest cells in the mesenchyme are?

A
  1. Choroid
  2. Sclera
  3. Corneal endothelium
    - neurocrest cells migrate into mesenchyme from neural crest and differentiate into the above structures

Head and Neck Anatomy (37 decks)

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