Anterior Segment Anatomy Flashcards
THE CORNEA
What does it do?
- Responsible for 70% of focusing power.
- Reduces optical aberrations.
- Protects against physical, chemical and infective agents.
THE CORNEA
How does it work?
- Very sensitive to touch & foreign bodies.
- Needs effective & constant tear film.
- There is no Corneal blood supply - nutrition is supplied from tear film (anteriorly) and aqueous fluid (posteriorly).
THE CORNEA
What does it look like?
- Optically clear.
- Multi-layered.
THE CORNEA
What are the corneal layers?
- Anterior Corneal Epithelium
- Bowmans Membrane
- Corneal Stroma
- Dua’s layer
- Descemet’s membrane
- Endothelium
THE ANTERIOR CHAMBER
Where is it?
- Between the Cornea and Iris.
THE POSTERIOR CHAMBER
Where is it?
- Between the Iris and Lens/Suspensory Ligaments.
AQUEOUS FLUID
Where is it produced and where does it go?
- Produced by the Ciliary body in the Posterior Chamber.
- Flows anteriorly through the Pupil.
- Flows out via the Anterior Chamber/Iris Angle.
THE IRIS
What is it?
Where is it?
- A thin pigmented diaphragm.
- In the Anterior Chamber that is visible through the clear Cornea.
THE IRIS
What does it do?
- Iris pigmentation determines the “colour” of the eye.
- The centre of the iris forms the Pupil, which dilates and constricts to regulate light reaching the Retina.
THE IRIS
What are it’s regions?
- The Pupillary zone is the inner region, the edge of which forms the boundary to the Pupil.
- The Ciliary zone is the rest of the iris that extends to it’s origin at the Ciliary body.
THE IRIS ANGLE
What is it?
Where is it?
- The Iris Angle is the relationship between the Cornea and Iris.
- The Angle is formed at the insertion of the Iris into the Corneo-Scleral junction.
THE IRIS ANGLE
What does it do?
- The Iris angle is critically important for the normal outflow of Aqueous fluid out of the eye.
THE IRIS ANGLE
What is the difference between a normal & abnormal Iris Angle?
- A normal open angle allows Aqueous fluid to drain from the Anterior Chamber into the Trabecular Meshwork.
- A narrowed or “closed Angle” can be caused by a shallow Anterior Chamber, Iris crowding with a dilated pupil or an abnormally forward lens position.
- A closed angle prevents outflow of Aqueous fluid, increasing Intraocular Pressure.
MYDRIASIS (DILATING THE PUPIL)
What muscles control pupil dilation?
- Radial dilator.
- Circular sphincter.
MYDRIASIS (DILATING THE PUPIL)
What do Sympathomimetics do?
- Sympathomimetics (e.g. Phenylephrine).
- Stimulate the radial dilator muscles.
- to “pull” the Iris open.
MYDRIASIS (DILATING THE PUPIL)
What do Parasympatholics do?
- Parasympatholics (e.g. Tropicimide, Cyclopentolate and Atropine).
- Paralyse the Circular Sphincter muscles.
- To “relax” the Iris, allowing it to open.
THE CRYSTALLINE LENS
What is it?
- Flexible & transparent.
- Has a Biconvex shape which is flatter at the front than at the back.
- Comprises Anterior & Posterior Capsules, Cortex and Nucleus with Epithelium lining the inside of the Anterior capsule.
THE CRYSTALLINE LENS
What does it do?
- Refracts (focuses) light to produce a clear retinal image.
- 30% of total refracting power of the Eye.
- Defects of the lens cause visual symptoms and can prevent effective imaging of the Vitreous and Posterior Segment.
ACCOMMODATION
What is it?
- The ability to adapt between distance vision and reading vision.
- Achieved by changing the shape of the lens.
- Usually declines with age.
THE CRYSTALLINE LENS
What structures does it have?
- Anterior Capsule Surface
- Epithelial cells
- Equator
- Cortex
- Posterior Capsule Surface
FOCUSING ON A DISTANT OBJECT
What happens to the lens?
- A relaxed ciliary ring tightens and produces a flattened lens.
