L49 Iris Flashcards
What is the pupilary zone?
The bit of the iris closest to the pupil
What is the Ciliary zone?
The bit of the iris closest to the ciliary body
What is the collarette?
The bit of the iris where the pupillary zone merges into the ciliary zone
Familiarise yourself with this clear diagram.
What can you not see in the diagram?
Ora Serrata and structures further to the left.
Where is the iris thinnest?
Where it comes off the ciliary body - this is known as the iris root.
Where is the iris thickest?
In the region of the collarette
What is the back surface of the iris covered in and how does that relate to the ciliary body.?
Present at the back surface of the eye is the Posterior double pigmented epithelium.
The ciliary body contains a double pigmented epithelium that merges at the iris root with the double epithelium at the back of the iris.
What is the difference between the bilayer epithelium of the ciliary body and the back surface of the iris?
The bi-layer epithelium of the ciliary body contained an outer pigmented layer and inner unpigmented layer whereas, the bi-layer epithelium of the iris contains two pigmented epithelium. (no unpigmented layer in the back surface of the iris.
Why are both layers of the back surface of the iris pigmented?
The function of the iris is to make the pupil (aperture stop) thus you want it to block light
It is to stop light getting through so that the pupil can act as an aperture stop.
How are pigment epithelial layers of the iris held together and why?
Interdigitating microvilli between pigment epithelial layers of the iris as well as adhering junctions, gap junctions, and desmosomes.
These exist as the iris is constantly contracting and expanding and so you don’t want these layers to separate.
What is that ring of pigment around the pupil of the eye?
It is called the pupillary ruff. It is the double pigmented epithelium from the rear surface of the iris that ‘peeps’ up through the iris.
(everyone has this even those with blue or other coloured eyes).
What does the pupillary ruff look like in person?
Why is the iris dilator/dilatator (you can refer to it as either one of the two) unusual (not unique)?
Because the dilator muscle is within the epithelial cells. Said to be myoepithelial.
How do the two layers of the rear surface iris epithelium differ?
The most posterior epithelial layer is 100% pigmented whereas the anterior epithelial layer is half pigmented half dilator muscle (it is myoepithelial).
What kind of muscle is the iris dilator muscle?
And what is it innervated by?
A radial muscle and its contraction thus results in pupil dilation.
It is smooth muscle so it is innervated by the autonomic nervous system and is innervated by the sympathetic system.
(to remember this think - wide-eyed with fear- to associate with the sympathetic system).
Connective tissue can either be dense or loose - depending on what?
Depending on whether collagen is tightly packed toegther or loosely arranged.
What kind of muscle is the iris sphincter muscle and where is it located?
It is a smooth muscle (circular muscle) and it is located at the tip of the iris (different to dilator muscle as its not part of the epithelium).
When the pupil is constricted how are the vessels?
They run roughly straight as can be seen in a fluorescine angiogram (basically putting flurorescine in to see a structure and then examining under UV light).
What is the anterior border layer of the iris made up of and where is it located?
The location is in the diagram for reference.
It is made up of a dense layer of fibroblasts underneath which is a dense layer of melanocytes.
