Week 7: Ocular Embryology 1 & 2 Flashcards
What is Neurulation?
Where flat disc (2D) begins to fold to form a hollow cylinder (neural tube that will form brain, spinal cord and retina) of 3 germ layers (ectoderm, mesoderm, endoderm)- occurs at end of 3rd week (days 18 to 28)
- start of nervous system
- as neural tube forms, some ectodermal cells migrate to form neural crest (several layers of cells which become areas of the eye) and which all become all sensory neurones
What are the primary brain vesicles?
- Develop in week 4
- Prosencephalon (forebrain), Mesencephalon (midbrain) & Rhombencephalon (hindbrain)
What are the 5 distinct regions of the CNS by the end of the 8th week?
- Forebrain: develops into the cerebrum
- Diencephalon: thalamus, hypothalamus, pituitary & pineal glands
- Midbrain: corpora quadrigemina (superior & inferior colliculi)
- hindbrain: pons, medulla & cerebrum
- spinal cord
When does the major development of the eyes take place and what does it involve?
- 3 to 10 weeks
- involves the Neural Ectoderm (ectoderm of neural tube) = retina, optic nerve fibres, iris eventually
- surface ectoderm = lens, conjunctival & corneal epithelia, eyelids and lacrimal apparatus (lacrimal glands + draining apparatus
- Mesenchyme = corneal stroma, sclera, choroid, ciliary muscle, parts of vitreous, muscles lining anterior chamber
what happens in the formation of the optic cup and lens at week 3-4?
Day 22 (week 3), a pair of shallow grooves form on each side of the invaginated forebrain (optic grooves)
-As neural tube closes, grooves become bumps on each side of the forebrain- the optic vesicles
-Optic vesicles extend from forebrain and grow toward surface ectoderm, their connections (optic stalks) become thinner (will become optic nerves)
-The proximity of optic vesicles to surface ectoderm induces it to thicken into the lens placode, which invaginates to become a lens pit
-Lens pit forms a circle that pinches off (from surface ectoderm) to become the lens vesicle
-When the lens matures later on, distal end of hyaloid artery will disintegrate and proximal end will persist (as central retinal artery)
When does the optic cup form?
-week 3-4 at the same time as the lens vesicle is forming, optic vesicle invaginates to form a double-layered structure, the optic cup
What is the development of the layers of the retina from the cells of the optic cup?
Cells of the optic cup’s outer layer produce melanin (pigment), and it ultimately becomes the retinal pigment epithelium (RPE)
• Cells of optic cup’s inner layer proliferate and generate glia, ganglion cells, interneurons, and photoreceptors. Collectively, the neural retina
• Retinal ganglion cells = neurons that send retinal electrical impulses to brain. Their axons converge at optic disc (blind spot) and travel down optic stalk. (This stalk is then called the optic nerve).
What protein does the lens cells synthesise?
Crystallin, does not exist anywhere else on body, lens differentiates at around 5-6 weeks
- human lens about 90mg at birth and mass increases at 2mg per year as new fibres form throughout life
- oldest fibres (in centre) gradually become less malleable and lens nucleus more rigid, causing progressively reduced accommodation (presbyopia) - need reading glasses
What is the hyaloid artery?
Branch of ophthalmic artery and in the optic stalk its function is to supply nutrients to developing lens
When does lens grow independent of blood supply?
Week 10
What month does the hyaloid artery regress and the proximal portion becomes the central retinal artery?
7th month
-regression of the hyaloid artery results in cloquet’s canal
What is Mittendord’s dot?
Small, pinpoint like scar on posterior surface of the lens
What is Bergmeister’s Papilla?
Small remnants of hyaloid artery may remain on optic disc
What are floaters?
Free remnants in vitreous humour, clumps of collagen and debris
