Ocular Anatomy 7 Iris Flashcards
When does the closure of the embryonic fissure occur?
33-35 days
What does abnormal closure of the embryonic fissure cause
Iris coloboma/hypoplasia
What are sphinctor and dilator muscles and bilayered iris epithelium derived from?
Neuroectoderm
Sphincter and dilator muscles arise from the anterior epithelial layer
When does pigmentation begin?
Posterior epithelium originally unpigemented
Fourth month of gestation, begins at pupil margin and spreads peripherally
Describe the structure of the iris
Pigmented diaphragm that consists of a posterior bilayered epithelium and an anteiror stroma rich in melanocytes and fibroblasts (muscle CT and fibroblasts)
- melanocytes produce piment which result in colour of iris
What is the collarette
2mm from pupil margin
Thickest region of the iris, divides it into pupillary and biliary zone
Where are the muscles of the iris located?
Sphincter pupillae located in the pupillary zone - concentrically arranged
Dilator pupillae in peripheral ciliary zone - radially arranged
Autonomic smooth muscles
What type of epithelium forms iris epithelium?
Bilateyed cuboidal epithelium
Cells lie apex to apex
Anterior layer (continuous with outehr pigmented layer of the ciliary epithelium - lacks in melanocytes)
Posterior layer is heavily pigmented
What is ectropion uveae
Basal processes of anterior epithelial cells give rise to the myoepithelial cells of the dilator muscle
Pigmented posterior epithelium extends anteriorly to the ruff but any further excursion is ectropion uveae
What is the blood supply to the riis?
Long posterior ciliary arteries with communication from the 7 anterior ciliary arteries
form major arterial arcade
Smaller arteries branch off in radial pattern towards pupil margin
What is the vneous drainage of the iris
Minor venous arcade join to form vortex veins
Are the iris vessels permeable?
Iris vessels are non-fenestrated and contain tight junctions betewen endothelium
This is a pseudo blood ocular barrier as in inflammation, white cells and proteins can leak out
Note: Ciliary body vessels are fenestrated
What is the nervous supply to the sphincter pupillae
Parasympathetic nerves
Arise from Edinger Westphal nucleus in midbrain and trauvel with oculomotor nerve to the orbit where they synapse in ciliary ganglion
Short ciliary nerves to supply ciliary and sphincter muscles
What is the nervous supply to the dilator pupillae
Long ciliary nerves from the nasociliary nerve and sympathetics from the internal carotid plexus (superior cervical ganglion)
