Flashcards in Exam 3 Remington- Embryology Deck (170):
What are the reasons for studying the development of the eye?
Adult anatomy explained, histology of ocular tissue, congenital abnormalities explained, congenital anomalies are more prevalent since more premature and high risk babies surviving
What are the steps after fertilization?
Fertilization -> Morula (solid mass) -> Blastula -> Inner cell mass (implanted in uterine wall about 10 day) -> Embryonic plate
Increase in number of cells
Move to new location
Process by which a cell acquires specific functional and structural characteristics
The influence a certain region of tissue or developing structure has on the development of another structure
When is the embryonic plate formed?
CNS, epidermis of skin, exocrine glands, inner ear, hair and nails
CT, skeletal system, muscle, dermis of skin, circulatory system
lining of alimentary and respiratory tracts
The ectodermal part of embryonic plate that will become CNS
When does thickening occur in ectoderm?
When is the neural tube formed?
The neural ectoderm forms the ____
The surface ectoderm covers the ______
Neural crest cells separate from ____ ____
What is formed from the neural ectoderm?
RPE, neural retina, optic nerve fibers, neuroglia, epithelium of ciliary body, epithelium of iris, iris sphincter, dilator muscles
What is formed from the surface ectoderm?
Lens, corneal epithelium, conjunctival epithelium, epithelium of eyelids, cilia, Meibomian glands, glands of Zeis and Moll, epithelium lining nasolacrimal system
What is formed from the neural crest cells?
Corneal stroma (which gives rise to Bowman's layer), corneal endothelium (which gives rise to Descemet's), most of sclera, trabecular structures, uveal pigment cells, uveal CT, ciliary muscle, meninges of optic nerve, vascular pericytes
Where is the mesoderm located?
Between ectoderm and endoderm
Includes both neural crest and mesoderm
The neural tube will form _____
When do optic pits become optic vesicles and out-pouches from diencephalon form?
Region joining optic vesicle to neural tube constricts
Inferior region of the vesicle and stalk begins to invaginate and forms a cleft
Also called fetal fissure or embryonic fissure
Incomplete closure of fissure, will result in incomplete formation of certain structures and/or layers
What is a thickening in the surface ectoderm?
What forms the lens plate or placode?
What gene may be one of the factors that extablishes the lens component of surface ectoderm?
An indentation of the lens vesicle forms ___ ___
When does the vesicle separate from the surface ectoderm?
Lens vesicle cells secretes what?
What elongates forming embryonic nucleus?
Posterior lens epithelium
What forms secondary lens fibers of the fetal nucleus?
Mitosis at the pre-equatorial zone
What are the vessels that enter the globe through the fissure formed from?
Posterior tunica vasculosa lentis branches from what?
Anterior tunica vasculosa lentis branches from what?
The posterior and anterior tunica vasculosa lentis are joined and nourish the lens during months ____
When are the networks absorbed?
The hyaloid arterial system is surrounded by ___ ___
The amount of reabsorption of glial tissue influences ____
What occurs in the optic cup?
Proliferation, migration, and differentiation
What is the first retinal layer to differentiate?
Neural Retina Proliferative Zone
Contains the cell bodies which will form retinal cells
Neural Retina Marginal Zone of His
Located next to basal lamina
Inner neuroblastic layer
Contains cells that will become ganglions, amacrines, and Mullers
Outer neuroblastic layer
Contains cells that will become photoreceptors, bipolars, horizontals (origin of interplexiform neurons not determined)
Transient fiber layer of Chievitz
Area between layers contains no cells
When does apoptosis begin?
What happens in retinal development during month 6?
No further mitosis, differentiation and cell maturation continue
The macular area is the thickest retinal area until about ____ months of gestational age and until up to 9 rows of ganglion cells present
The depression in the macula continues to deepen until when?
What are first to differentiate in the macular area?
What are cone axons dependent on?
Light stimulation for complete growth of Henles fibers to reach synapses in OPL
What does the CRA develop as buds from in month 4?
What does the CRV develop as buds from?
When is the vasculature complete?
3 months post pardum
What does the corneal epithelium develop from?
When are ZO evident in the corneal epithelium?
What does the corneal endothelium develop from?
Develops from neural crest cells in 1st wave mesenchyme
What does the corneal stroma develop from?
From neural crest cells in second wave of mesenchyme
Where does the sclera form from?
Primarily from the neural crest, in mesenchyme that surrounds optic cup
By what months has the sclera surrounded the choroid?
The sclera usually develops _____ first
Where does the choroid develop from?
What is the first layer to differentiate of the choroid?
The epithelial layers of the ciliary body are from the ____ ___
The mesenchymal cells in the ciliary body differentiate forming what two things?
Stroma and muscle
When will the annular muscle of Muller be completed?
1st several months after birth
What do the iris epithelial layers form from?
____ _____ forms from a group of cells that detaches from the anterior iris epithelium
Mesenchymal cells differentiate in the iris forming _____ and _____
Melanocytes and fibroblasts
When the anterior tunica vasculosa lentis degenerates into what two things?
Minor circle of the iris and stroma
_____ ____ forms from cells of third wave of mesenchyme
When does the pupillary membrane present?
The pupillary membrane degenerates from month _____
The remnants of the pupillary membrane are incorporated into what two things?
Collarette and anterior border layer
Mass of _____ accumulates in the angle area
Once the trabecular meshwork is formed a continuous sheet of _______ covers it
When must the trabecular meshwork break down exposing the meshwork for aqueous drainage to occur?
What does Schlemm's canal develop from?
Veins in the area
What is the primary vitreous?
Degenerating hyaloid system becomes Cloquet's canal
What is the secondary vitreous?
Mesenchyme, retinal fibrils forms intermediate vitreous
What is tertiary vitreous?
What is the outer layer of the optic nerve?
Forms neuroglial sheath
What is the inner layer of the optic nerve?
Cells form glial tissue, other cells vacuolate allowing for passage of ganglion axons
_____ ____ fill lumen growing from the globe to the LGN
Where does myelination begin?
When is myelination completed?
1 month after birth
Eyelid buds grow and fuse when?
About 2nd gestational month
When do eyelids separate?
What of the eyelids is made of surface ectoderm?
Epithelial layers of the skin and conjunctiva, hair follicles and cilia, Meibomian glands, Zeis glands and glands of Moll
What of the eyelids is made of mesenchyme?
Tarsal plates, orbicularis, levator, and tarsal muscle of Muller
What part of the orbit has neural crest origin?
Fat and CT
What is the position of the orbit at month 3?
What is the position of the orbit at birth?
What is the position of the orbit in adulthood?
Muscle cells have ________ origin
Connective tissue has _____ _____ origin
The lacrimal gland was once thought to be derived from ___ _____, but now believed to be from ______ _____
Surface ectoderm, neural crest
The nasolacrimal system is not fully developed or functioning until what age?
All structures of drainage has ______ _____ origin
Day 1-21; rapid cell division, differentiation of primary germ layers, travel down fallopian tubes to uterus where implantation occurs about day 10
4-8 weeks; differentiation of all major internal and external body structures, vital organs first
9 weeks to birth
What happens in the fourth week of the embryonic period?
Cardiovascular system, heart starts beating
What happens in the fifth week of the embryonic period?
Eyes, ears, mouth, and nose forming
What happens in the 5-8 weeks of the embryonic period?
Limbs, fingers, and toes are webbed
What happens in week 12 of the fetal period?
Growth stage, sexual differentiation
What happens in week 28 of the fetal period?
Brain wave patterns show active cycles
When is the age of viability?
How long is a normal term?
GA 7-8 days
GA 11-12 days
GA 21-24 days
GA 24-27 days
GA 5 weeks
GA 6 weeks
GA 7 weeks
GA 8 weeks
GA 3 months
GA 4 months
GA 5 months
GA 6 months
GA 7 months
GA 8 months
GA 9 months
slight departure from normal, too minor to interfere with function
Very different from normal, may interfere with function
Difference in structure which does not resemble any stage of normal development
Normal development halted
What are the causes of ocular congenital abnormalities
Genetic, environmental, interactions between genetic and environment
Any agent which acts on the fetus during intrauterine life, may be chemical (drugs), disease, physical, nutritional
What is likely is insult during the germinal period?
What is likely if insult during embryonic period?
Major anomalies or aberrations
What is likely if insult during fetal period
Minor anomalies and variation
Single median eye or 2 fused at midline
Greater than normal distance between orbits
Less than normal distance between orbits, midbrain often affected
Absence of ocular tissue derived from optic cup
Globe and lens small and undeveloped
Congenital glaucoma, marked distention of eye caused by increase of IOP, cause is often defect in angle structures or persistence of Barkan's membrane
What is the outcome of buphthalmos?
Endothelial compromise in buphthalmos leads to what?
Corneal edema and scarring
What happens if there is nerve fiber loss in buphthalmos?
Lack of pigmentation, normal development of sensory retina is influenced by melanin-related agent in RPE, absence of pigment causes retinal abnormalities are present, underdeveloped central retina, fewer rods
Cornea and anterior segment enlarged, may be associated with increased IOP
11 or 12 mm, normal size globe, small cornea
Small area of tissue on the posterior lens, no visual implications
Associated with genetic, metabolic, or infectious agents, viral infection of the mother during the first trimester, effect on VA depends on extent, visually debilitating cataracts, soft CL have been used successfully in infants and IOLs have been used in children as young as 3 years
A remnant of the glial tissue of the hyaloids system, glial tissue projects from optic nerve head, no visual implications
Optic nerve hypoplasia
Optic nerve fails to develop completely, fewer than normal number of axons, failure of ganglions to differentiation, failure of their axons to reach the optic stalk, often associated with CNS developmental problems or endocrine disorders, cognitive difficulties and multiple handicaps are common
Persistent hyperplastic primary vitreous
Failure of the hyaloid arterial system to regress, appears as a white retrolental mass, associated with angle closure glaucoma and cataract formation
Persistent pupillary membrane
Remnant strands form the pupillary membrane, usually attached to collarette, no visual implications
Failure of iris to form
What are 3 congenital defects affecting the retina?
Myelinated or medullated nerve fibers, coloboma of internal structures, retinoblastoma
Ranges from insignificant chorioretinal defect to complete involvement of interfior retina and choroid, causes VF defect
What is the most common malignant tumor in childhood?
How frequent are retinoblastomas?
1:17,000- 1:34,000 live births per year, 350 new cases in US per year
How does a retinoblastoma occur?
Can be dominantly inherited condition with poor or sporadic penetrance or a new genetic mutation, genetic counseling is mandatory
Is retinoblastoma bilateral or unilateral?
Both, bilateral is always inherited
Retinoblastoma tumor is often derived from malignant changes in _______
What is the presenting sign of a retinoblastoma?
White pupillary reflex, the tumors appear as white mass, may seed into vitreous or anterior chamber
What are treatment options for retinoblastoma?
Photocoagulation, cryotherapy or radiotherapy, chemotherapy
Large tumors or optic nerve involvement require ________
What are congenital defects affecting vasculature?
Sturge-Weber syndrome, retinopathy of prematurity
Nevus of skin of face (often called port-wine stain, ocular manifestations include hemangiomas of choroidal BV's, may have diffuse leakage leading to retinal detachment
What is retinopathy of prematurity associated with?
Low birth weight and supplemental oxygen therap