Ocular: Uvea (Iris) Flashcards
Which tunic is the uvea located in?
The middle tunic/vascular tunic
Is the uvea pigmented?
Yes
What is the uvea composed of?
Iris, ciliary body, choroid
What is the average iris diameter?
12mm
What value and direction is the pupil decentered?
0.5mm inferonasal to the iris center
What is the range of pupil diameter in NORMAL patients?
1mm(light)-9mm(dark)
What are the two major zones of the iris?
-ciliary zone (C)
-pupillary zone (P)
What is the pupillary ruff?
A continuation of the pigmented epithelium
What is the collarette?
A circular ridge raised 1.5mm from pupillary margin and is the division between the pupillary and ciliary zones
What did collarette used to be?
Old fetal pupillary membrane attachment site
What are the crypts of the iris?
Where the iris is missing the top layer (anterior border)
What is the iris root?
The attachment point of the iris to the ciliary body
Does the iris color typically differ between pupillary and ciliary zones?
Yes
Is the anterior border layer an epithelium?
No!
What is the anterior border layer (ABL) made up of?
A meshwork of interweaving cells that have fibroblasts and melanocytes
Is the anterior border layer (ABL) permeable to aqueous?
Yes
What is the iris color dependent on?
The amount of melanin granules within the ABL melanocytes
What is the function of iris crypts?
Enable quick aqueous entry and exit from the stroma as the iris volume changes with miosis and mydriasis
Two types of iris crypts:
-peripheral crypts
-Fuchs crypts (on each side of collarette)
What is the iris stroma continuous with?
The stroma of the ciliary body
What is the iris stroma permeated by?
Aqueous humor
What types of collagen make up the iris stroma?
Type I and type III
What immune cells are located in the iris stroma?
-mast cells
-macrophages
-dendritic cells
What vasculature is located in the iris stroma?
radial branches from MACI
Is the iris stroma vasculature fenestrated?
No
What type of muscle is teh iris sphincter muscle?
Circular SMOOTH muscle
What is the function of the iris sphincter muscle?
Miosis -> constrict pupil
**parasympathetic control
Where is the iris sphincter muscle located?
In the pupillary zone of the stroma
The iris epithelium is made up of ___ layers but is NOT a typical compound/stratified epithelium
2
How are th layers positioned in the iris epithelium?
Apex to apex
What muscle is located in the anterior iris epithelium?
Myoepithelium (iris dilator muscle)
Where do the iris dilator muscle fibers of the anterior epithelium run?
From iris root to about the midpoint of iris sphincter muscle
What is the function of the iris dilator muscle?
Mydriasis -> pupil dilation
**sympathetic control
What is iridodialysis?
A tear at the iris root secondary to trauma
What is the thinnest part of the iris?
Iris root
Where is the iris root in relation to the limbus?
Just peripheral to the limbus
How can you diagnose very tiny root tears?
Gonioscopy
How can you distinguish iridodialysis?
-Iris body is next to the root
-flaccid
-“D” shaped pupil
Two iris epithelial layers:
-anterior myoepithelium
-posterior pigmented epithelium
What two portions make up the anterior myoepithelium?
Basal and apical portions
What makes up the Basal portion of anterior myoepithelium?
Elongated layers of smooth dilated muscle fibers
What makes up the apical portion of the anterior myoepithelium?
Pigment with traditional cellular organelles
How is apical portion of anterior myoepithelium connected to posterior epithelium?
Tight junctions
What are some characteristics of the posterior pigmented epithelium of the iris?
-cudoidal shaped
-impermeable tight junctions and interdigitatins between cells
In the spaces between cells, what extends off the apical ends?
Microvilli
What is the only portion of the anterior epithelium that contains melanin granules?
Apical portion only
Where are melanin granules located in the posterior epithelium?
All throughout!
What happens in the iris when dilated?
-sulcus forms at collarette
-ciliary portion thickens (pupillary portion doesn’t)
-iris root thickens MINIMALLY (so angle not occluded)
Which muscle does diabetes affect?
The iris dilator muscle
Why does iris dilator muscle lose function in diabetic patients?
Glycogen accumulates in both epithelial layers which reduces myoepithelial function
What does the pupillary ruff “cure”together
both epithelial layers at the pupillary margin anteriorly
What is the termination point of ABL?
Pupillary ruff
What is ectropion uveae?
Iris pigmented epithelium found on the anterior iris surface
What is Congenital ectropion uveae
Neural crest migration abnormality that can also affect the muller muscle
Acquired ectropion uveae
Inflammatory or ischemic process
What is located in posterior iris surface?
-contraction furrows of schwalbe
-structural folds of schwalbe
-ciliary processes
Sympathetic innervation of iris dilator muscle:
Write out
Parasympathetic innervation of iris sphincter muscle:
Write out
Functions of the pupil:
-control of retinal illumination
-reduction in optical aberrations
-depth of focus
Why does pupil narrow with age?
Iris dilator muscle weakens
How does pupil reduce optical aberrations?
By reducing light from entering through peripheral parts of lens and cornea
How does pupil control retinal illumination?
By constricting to limit after images in bright light settings
Pathway or vasculature in the iris:
Anterior ciliary arteries and long ciliary arteries combine to form the MACI which give off radial arteries (which supply iris!)
What do the radial arteries form/connect to?
Minor arterial circle of iris that give off capillary arcades
Are Iris vessels large?
Yes, they have connective tissue sheath around endothelium
What is the function of the sheath around the vessels?
-prevent kinking during dilation to preserve blood flow
-anchor vessels in place
Blood vessels _______ to provide slack
Meander -> straighten during miosis and curved during dilation
What causes Heterochromia?
-Sympathetic input causing trophic effect on the iris pigmentation
-suspect interruption of input
What colored eyes are more susceptible to Horner’s syndrome?
Light colored
What is ocular melanocytosis?
Excessive melanocytes in ABL which leads to increased risk of uveal melanoma
Why are eyes pinkish-blue in albino?
-ALL layers of the iris lack pigment
-blood vessels and red chorioretinal reflex are seen
What chromosome is responsible for Iris color?
Chromosome 15
What is visible in blue eyes?
Blood vessels and radial collagen fibers
Arterioles-venous malformation:
Artery-> vein without a capillary bed
What are brusfield spots or kunkmann-wolffian bodies?
Tiny whiteish-yellowish nodules of ABL hyperplasia enclosed by ring of hypoplasia
-brusfield = Down syndrome
-kunkmann = no genetic issue
What are lisch nodules?
Melanocytes hamartomas where the is an atypical high number of focal pigmented harmartomas
What is Nevus?
Accumulation of melanocytes in the ABL, can be multiple or cover an iris sector
What are iris mamillations?
Regularly spaced elevations that are the same color and can be associated with ocular melanocytosis
