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)
What is the timeline for the hyaloid artery?
Hyaloid artery grows from the ophthalmic artery anteriorly to the lens, develops by week 8, then begins apoptosis in month 4. Blood stops flowing through the artery in month 7 and it detaches from the optic disc in month 8
What is the name of the structure that is seen when the hyaloid artery doesn’t fully detach from the optic disc?
Bergmeister’s papillae
What is a Mittendorf dot?
A remnant of the hyaloid artery system left on the back of the lens
What is Persistent Hyperplastic Primary Vitreous (PHPV)?
failure of the primary vitreous to fully degenerate into Cloquet’s canal, resulting in excess material throughout the canal and blocking the visual axis. Leads to vision degradation and secondary glaucoma
T/F: the central retinal artery and vein which supplies the inner retina derives from the hyaloid system
True! When the hyaloid artery on the lens begins to degenerate (month 4), the vessels from the optic nerve head start to spread out into the periphery reaching to the ora serrata (nasally at month 8 and temporally month 9)
When is the mature pattern of capillaries in the eye formed?
3 months after birth
What is retinopathy of prematurity?
retinal vasculature is not completely grown in premature infants, who are often on supplemental oxygen which then triggers normal vascularization to stop and cause abnormal vascularization to begin. causes increased risk for RDs! can treat with cryo
What is a coloboma?
a developmental disorder where the fetal fissure along the inferior nasal section of the optic cup/stalk does not properly seal as it should (around weeks 6 or 7)
What is the timeline for the development of the foveal pit?
Foveal pit begins to develop around month 7 and continues until 11-15 months after birth. the density of cones increases and the size of the rod-free zone decreases until about 5 years after birth
How do the RPE and neuroretina develop?
From the optic cup, the RPE continues to grow and the neuroretina differentiates its cells in an asymmetric pattern, begins at the central retina and extends peripherally. there is no firm connection between the two layers (subretinal space) which allows them to grow. Mitotic division stops at birth when there is a large increase of oxygen concentration
How does ocular albinism occur?
The macula is underdeveloped due to having less pigment available (normal pigment is necessary for neurosensory retina development), this also occurs with an abnormally large number of crossed fibers in the optic nerve and may result in binocular issues
How does the choroid develop?
3 waves, outer network forms the choriocapillaris which is supplied during month 3 by SPCAs, veins that will become vortex veins also begin to form in month 3, and the middle layer of the choroid develops in month 4 for arterial connections. The choroid is fully differentiated and becomes pigmented around month 7
T/F: The eyelids fuse together at month 3 and then split apart in month 5
True
What is the timeline for the development of the nasolacrimal system?
Becomes patent in month 6 but continues to develop for a few years after birth
What is the average PD at birth?
~49mm
What tissues does the ciliary body derive from?
epithelium is neuroectoderm
muscle is neural crest cells
What tissues does the iris derive from?
Anterior/posterior pigmented epithelium and the iris sphincter/dilator is neuroectoderm
Iris stroma is neural crest cells
