BS - Anterior Chamber - Week 3 Flashcards
What is the normal intraocular pressure?
10-20 mmHg.
Define the anterior chamber angle. From what structure on the anterior surface of the eye can it be reached?
The junction between the iris and cornea.
Can be reached from the limbus, directly deep.
What is the scleral sulcus, and what is its anterior border?
What bridges the sulcus?
The sulcus is the inside surface of the limbal depression. The anterior border is the canal of Schlemm.
The trabecular meshwork bridges the scleral sulcus.
What is the scleral spur? What is its purpose?
The posterior border of the scelral sulcus. Prevents the canal of Schlemm from collapsing under cilliary muscle contraction.
What is Schwalbe’s line? Is it precisely defined? What transition happens here?
The point on the cornea where Descemet’s membrane ends.
Is a smooth transition, and not a defined sharp line. Transition from endothelium to trabecular meshwork occurs.
What forms the trabecular meshwork?
Connective tissue beams enclosed by trabecular cells.
What are the inner layers of the trabecular meshwork like?
Plate-like cribriform
What does the outer layers of the trabecular meshwork form?
Lamellated meshwork
Which areas of the trabecular meshwork drain/dont drain?
The anterior border of the meshwork is non-draining.
The posterior trabecular meshwork is where the bulk of draining occurs.
Name and describe the two zones of the lamellated meshwork.
Uveal - ropelike, large irregular openings
Corneoscleral - sheets perforated by elliptical openings
Describe the deepest layer of the trabecular meshwork. What kind of network does it contain, and what is it continuous with?
Juxtacanalicular (cribriform) - sieve-like plates
High resistance
Has a network of elastic fibres, continuous with the ciliary muscle tendons.
Where do ciliary muscles insert, and what is a consequence of ciliary muscle contraction?
They insert into the juxtacanalicular/cribriform plexus.
Contraction results in the widening of their intercellular spaces.
What do cells of the trabecullar meshwork produce, and how is the meshwork cleaned of debris?
They produce GAGs, glycoproteins, and fibrils.
Are highly phagocytic, removing debris from the meshwork.
What lines the canal of Schlemm?
Endothelial cells.
How does the bulk of the aqueous humour reach the canal of Schlemm?
The formation of giant vacuoles within the endothelial cells.
Describe the 5 steps of trabecular outflow.
- Through the trabecular meshwork
- Through Schlemm’s canal
- Through external collector channels of Maggiore
- Through the deep intrascleral venous plexus
- To the episcleral veins and vortex system
Aqueous humour flows from the anterior chamber to the episcleral veins. What is the pressure within these structures?
Episcleral veins - 9 mmHg
Intraocular pressure - 10-20 mmHg
Aside from the trabecular pathway of drainage, describe the second pathway, and the percentage of outflow it accounts for vs the trabecular pathway.
Uveoscleral pathway
Between uveal trabeculae and ciliary muscle bundles, aqueous humour is absorbed by blood vessels here, and drain to the episclera.
Accounts for 10-15% of aqueous humour drainage.
Trabecular pathway forms 80-85%.
Describe the effect of ciliary muscle contraction on the two aqueous drainage pathways.
Trabecular - opens trabecular pores, increasing drainage
Uveoscleral - Reduces space between ciliary muscle fibres, reducing drainage
What is a pupillary block, and when is it performed?
A laser is used to burn a hole in the iris, used when aqueous drainage is blocked.
What 5 anatomical abnormalities would predisposition an individual to obstructed aqueous outflow?
- Narrow anterior chamber angle
- Shallow anterior chamber depth
- Thicker lens
- Lens positioned more anteriorly
- Small corneal diameter/shorter axial length
What happens to the trabecular meshwork with age?
Accumulates with collagen, resulting in smaller pores, and decreased outflow.
Describe gonioscopy.
Using a 3-4 mirrored instrument to look at the anterior chamber angle.
During gonioscopy, describe the structures seen, going from superior to inferior.
Cornea Anterior chamber Schwalbe's line Trabecular meshwork Scleral spur Ciliary bodies Iris Pupil
Define glaucoma.
Increased intraocular pressure.
