Second Test 151210 Flashcards
Surface ectoderm, outcome and emryology:
Skin, mucous, membranes, glands
1) lens
2) epithelium of cornea
3) lacrimal gland
4) eyelid skin, lashes, glands
Neural ectoderm, outcome and embryology
CNS, retina
1) optical nerve
2) retina, pigment epithelium
3) pigmented and unpigmented epithelium of the ciliary body and the iris
Mesoderm develop into:
Muscle, bone, connective tissue
- vascular tissue: choroid, retinal vessels, vessels of EOM, lids, etc., hyaloid embryonic vessels
- connective tissues: sclera, corneal stroma (primarily), supporting ligaments, tendons etc.
- muscle tissue: ciliary, EOM, Levator, orbicularis oculi
Endoderm develop into
Lining of digestive system
The neural crest cells - outcome:
- corneal endothelium
- trabecular meshwork
- keratocytes of corneal stroma
- pupillary membrane (embryonic)
- stroma of the iris
The neural crest cells - outline the first migration wave (week 6)
Migration to the front of the eye cup, corneal epithelium and trabecular meshwork
The neural crest cells - outline the second migration wave (week 7)
- Between corneal endothelium and epithelium keratocytes
- In front of embryonic lens-pupillary membrane
The neural crest cells - outline the third migration wave (week 8-10)
Iris stroma
Outline the development of the sensory retina
1) early differentiation into zones - week 5
2) formation of temporary layers - week 6-11
- begins at central retina; outer-, inner neuroblastic and marginal layer
3) cell differentiation and migration - week 12-24
4) final organisation of layers - month 7-13
Foveal development:
Outline what happens during the 6th month
The ganglion cell layer thickens in the future macula
Foveal development:
Outline what happens during the 8th month
Differentiation proceeds rapidly in the retina, but not at the foveal region - causing a depression to appear
- rods do not develop here
Post natal maturation:
During what time does rapid development occur?
Birth -> 6 months after birth
Post natal maturation:
During what time does gradual development occur?
Until 3-4 years of age
Define bilaminar disc
towards the end of the 2nd week of gestation the embryo has 2 cell layers - an epiblast and a hypoblast (these are together called the bilaminar disc)
Hypoblast becomes:
the embryo
Epiblast becomes:
the extra-embryonic membranes (e.g. yolk sac)
What is the purpose of gastrulation?
To produce the 3 layers from which embryonic structures will develop (ectodem, endoderm and mesoderm)
From what day does eye development start
approx day 22
Define somites
- Paired segments along neural tube of a vertebrate embryo, next to the midplane
- Develop into vertebral column and muscles
- Good indicator of precise embryonic age
Embryology of the anterior segment:
Outline what happens in week 8
1) eye extends forward to form the iris
2) tunica lentis vessels surround the lens, major arterial circle of the iris is formed
3) anterior chamber forms and deepens
4) corneal stroma forms and develops backwards to form sclera
5) lid fold begins
Embryology of the anterior segment:
Outline what happens in week 10
1) anterior chamber deepens
2) continuing iris growth
3) eyelids fuse, conjunctiva enlarges
Embryology of the anterior segment:
Outline what happens in week 14
1) ciliary processes and zonules develop
2) ciliary muscle develops
Embryology of the anterior segment:
Outline what happens in month 4
Iris sphinctor develops
Embryology of the anterior segment:
Outline what happens in month 5
Iris dilator muscle forms
Embryology of the anterior segment:
Outline what happens in month 2-3
cornea develops its membranes
- descements membrane (posteriorly)
- Bowman’s membrane (anteriorly)
Embryology of the anterior segment:
Outline what happens in months 5-7
hyaloid system of vessels atrophies
Define uvea
The vascular layer of the eye, between the sclera and the retina
- made up of blood vessels in a loose network of connective tissue and pigment cells
- blood vessels -> circulation to the eye
- pigment -> prevent unwanted light entering the eye + reduces light reflections in the eye
Trophoblast differentiates and form:
Cytotrophoblast and syncytiotrophoblast
Outline the 3 structures of the Uvea
Iris
Ciliary Body
Choroid
What does the iris do?
rings the pupil + forms division between anterior and posterior chambers.
Controls amount of light reaching retina, depth of focus, + reduces aberrations
Outline the size and thickness of the IRIS
Diameter: 13mm
Thickness: 0.1mm at the root + 0.6mm at the thickest point (the collarette)
What is the collarette?
Part of the iris that divides the anterior surface into two zones:
- pupillary region
- ciliary region
Where is the pupil located?
in the iris, slightly down and in
What’s the diameter of the iris
can vary from 1mm to 8mm
Define mydriasis
dilation of pupil
Define miosis
Constriction of pupil
During mydriasis and miosis, which region alters the most in width:
Pupillary or ciliary?
Ciliary
Define Heterochromia
Large variations of colouration of the iris; different amount of pigmentation in the anterior surface
Iris structure:
What does the anterior border layer consist of
- fibroblasts, melanocytes and collagen fibers
Iris structure:
What does melanocytes contain?
granules of the pigment melanin
Iris structure:
What is the stroma composed of?
Connective tissue containing fibroblasts and pigment cells lying in a mucopolysaccharide matrix
Iris structure:
What does the stroma contain?
Iris vessels and sphincter muscle
Iris structure:
What is the sphincter pupillae muscle, and where is it located?
= a band of smooth muscle
- 0.75-1mm wide + about 0.1mm thick
- running parallel to the pupil margin
(In extreme miosis the muscle can be reduced to about 15% of its original length)
Iris structure:
What is the epithelium and its functions?
- a double layer that extends around the pupil margin
- both layers are deeply pigmented
- outermost layer carries contractile processes and form the dilator pupillae muscle
- densely packed with melanin
- posterior surface appears black and prohibits the passage of light
Outline the blood supply of the iris
- radial blood vessels - spiral course, enabling adequate movement during mydriasis and miosis
- arteries derived from the major arterial circle in the ciliary body, run through iris to anastomose in the minor iridic circle near the collarette
- capillary roots pass towards the pupil margin
Outline the blood drainage of the iris
- venous drainage same path back to the ciliary plexus, and then to the anterior ciliary veins/vortex veins
- these blood vessels also serve as a route of exchange for the metabolities and waste products of the aqueous humour
Outline the nerve supply of the iris
- sensory supply by nerve fibres that join the long/short ciliary nerves en route to the nasociliary branch of the ophthalmic division of the trigeminal nerve
- motor nerves are autonomic sympathetic and parasympathetic
- Parasympathetic from oculomotor (CN III) nerve - synapse with ciliary ganglion
- sympathetic from cells in the superior cervical ganglion
Outline the nerve supply of the sphincter
- parasympathetic innervation (miosis)
- dilator sympathetic innervation (mydriasis)
What is the thickest region of the iris?
the collarette
what is the thinnest region of the iris?
the iris root
Outline the structure of the uvea
1) iris
2) the ciliary body
3) the choroid
outline the functions of the ciliary body
- accommodation
- production of aqueous
- production of vitreous continents
What is the ciliary body?
highly vascular pigmented structure
outline the structure of the ciliary body
1) supraciliaris
2) stroma
3) epithelium
The ciliary body:
what is the supraciliaris?
- lines sclera from scleral spur to choroid with which it blends posteriorly
- a transition zone from ciliary stroma to the sclera
- consist of collagen + fibroblast + melanocytes
The ciliary body:
what does the stroma consist of?
- the stroma is filled by the ciliary muscle - extends from scleral spur to the choroid
The ciliary body:
what is the net effect of contraction of the ciliary muscle?
reduce tension on the suspensory fibres of the crystalline lens - producing accommodation
outline the types of smooth muscle fibres of the ciliary muscle
1) longitudinal fibres
- from scleral spur to choroid, run parallel to inner surface of sclera
2) radial fibres
- also called oblique fibres
3) circular fibres
- have sphincter like orientation close to the iris root
the stroma within pars plicata
pars plicata folded into 70-80 processes
- stroma within is packed with fenestrated capillaries that supply constituents for production of aqueous humour
The ciliary body:
outline what the epithelium consist of
- double layer of cells from iris root to retina
- deep layer consist of pigment
- superficial layer consist of unpigmented cells connected by desmosomes
