Choroid, Iris and Lens Flashcards
Why are both layers of the iris epithelium pigmented?
Absorb all the stray light
What sort of muscle is the iris dilator muscle and what is the orientation of the fibres?
It is a smooth muscle arranged radially and runs perpendicular to the pupil.
What is the effect of the contraction of the iris dilator muscle on pupil size?
Results in pupil dilation - widens the pupil
What is the orientation of the iris sphincter fibres and what is the effect of their contraction on pupil size?
It is a circular muscle and contraction leads to pupil constriction - decreases pupil size
What neurotransmitters are involved at the iris sphincter and dilator muscles?
Iris Sphincter = adrenaline
Iris Dilator =
Apart from muscle, what else do you expect to find in the iris stroma?
Loose connective tissue and widely spaced collagen fibres, fibroblasts and mast cells and blood vessels
What makes up the anterior border layer of the iris? How is this different to most other biological borders?
Fibroblasts
-There arent any epithelial cells lining the surface
What makes up the anterior border layer of the iris? How is this different to most other biological borders?
Fibroblasts
-There arent any epithelial cells lining the surface
What makes irises different colours?
The varying number and thickness of melanocytes
What is the nature and function of the pigment in the choroid?
To create a black box effect, minimising light scatter
To what structure do the choroidal capillaries supply nutrients?
RPE
How thick is Bruch’s membrane?
5 microns
To what structures to the short posterior ciliary arteries supply blood?
They supply blood to the choroid and iris
To what structures do the anterior ciliary arteries supply blood?
They supply blood to the superior, inferior and medial rectus as well as the conjunctiva and sclera
What is the compostition of the lens capsule?
It is a smooth transparent basement membrane composed of super helical collagen fibres
What gives the lens capsule its elasticity?
Due to superhelical (spring like structure) collagen
What is the function of the lens capsule elasticity?
To allow the lens to change shape during accommodation
How does the shape of the lens epithelium vary with location on the lens?
A the anterior pole, it is squamos, between the pole and the equator it is more cuboidal and at the equator its almost columnar
What process accounts for the nuclear bow in the lens equator?
epithelial cells elongate to become lens fibres
What happens to old lens fibres?
They remain in the lens, clump together and form opacities in the lens
What structures do lens fibres form when they join together on the anterior and posterior surfaces?
Sutures
Why is there a need for such a tight fitting organisation of the lens fibres?
So that all light passing through the lens is refracted
Why the requirement for gap junctions in lens fibres?
To allow nutrients to pass from cell to cell in the lens - cytoplasmic continuity
Whys is the stroma of the iris so insubstantial?
Widely spaced collagen fibres allow contraction
