Embryology of the Eye (Q3) Flashcards
What is the time frame for the embryonic period of development?
0-8 weeks gestation
What is the time frame for the fetal period of development?
8 weeks gestation to birth
What kind of malformations result when a complication occurs during the embryonic period?
Structural malformation
What kind of malformations result when a complication occurs during the fetal period?
Functional malformation
Ocular mesenchyme is made up of
Neural crest cells and mesoderm
What are the optic vesicle and optic stalk derived from?
Neuroectoderm along the mesencephalon of the neural tube
What does the mesoderm/mesenchyme develop into and in what order?
Mesoderm surrounds the optic vesicle and develops into the EOMs, firstly the ones innervated by CN3, then LR and then SO.
How does the lens develop and from which tissue type?
the lens placode comes from thickened surface ectoderm near the optic vesicle (day 27) and then later (day 33) the placode folds in and pinches off to create the lens vesicle
What tissue gives rise to eyelids and epithelium of cornea?
Surface ectoderm
What structures result from the multiple waves of neural crest cells that enter the eye in Week 7?
Wave 1 - corneal endothelium and trabecular endothelium
Wave 2 - keratocytes/corneal stroma
Wave 3 - iris stroma (but NOT the muscles)
What is the timeline for development of Descemet’s membrane vs. Bowman’s membrane?
Weeks 9-12 for first evidence of Descemet’s. Bowman’s doesn’t develop until the end of the 5th month
Which weeks is there rapid growth of mesenchymal tissue at the limbus to increase the corneal curvature?
Weeks 9-12
How does the trabecular mesenchyme form?
From mesenchyme in between the optic cup and lens/cornea. TM first develops in month 4, and then is uncovered from ciliary body/iris and corneal endothelium in month 7
How does Schlemm’s canal develop?
develops over 3 months, full completion in month 9, forms from the mesenchyme in between optic cup and the lens/cornea
What comes from the two layers of the optic cup?
Outer pigmented layer: ciliary epithelium, anterior iris epithelium, iris sphincter/dilator, RPE
Inner non-pigmented layer: nonpigmented ciliary epithelium, posterior pigmented iris epithelium, neural retina
(adhered at week 12)
When do the anterior ends of the ciliary processes attach to the sceral spur?
7.5 months
During months 4-6 ciliary channels appear where?
Between pigmented and nonpigmented ciliary epithelial cells (for aqueous humor reservoir)
How does the ciliary muscle form vs. ciliary body?
The primitive ciliary muscle fibers form from neural crest cells in month 3 and then orderly strands form in month 4. The ciliary body epithelial layers are formed from the neuroectoderm
Which tissue is the stroma of the iris formed from?
Neural crest cells
Which tissue are the iris sphincter and dilator formed from and when?
Both are developed from neuroectoderm, iris sphincter during months 5-7 and the dilator develops by the end of month 6
What may be the structural reason behind congenital glaucoma?
The ciliary body and iris should continue to slide backward for up to a year after birth, but if it remains more forward than it should, it may overlap the TM and block proper aqueous flow. Requires surgery to open the angle
How does the lens capsule form?
From the surface ectoderm that lies on the outer lens vesicle after it has detached
How does the lens nucleus form?
The cells of the posterior wall of the lens vesicle elongate to fill the center and meet with the anterior cells to form the embryonic nucleus. The anterior cells then migrate to the equator and extend fibers that meet and form the sutures, secondary fibers form Y-sutures, and the fetal nucleus forms around the central embryonic nucleus
What does the vitreous form from?
Mesenchyme, firstly in week 5 and then second form in week 6 (second form pushes primary vitreous and hyaloid system into Cloquet’s canal)
