Anterior chamber Flashcards
What are the borders of the anterior chamber?
Corneal endothelium to anterior ciliary body, iris and lens
What is the average depth of anterior chamber?
3.15mm
What is the volume of the fluid contained in the anterior chamber?
0.2mL
What is the first structure to disappear on gonioscopy if anterior chamber angle narrows?
Anterior ciliary body as it just pokes up at the very edge of the angle
Where does the scleral spur run?
It runs posterior to the canal of Schlemm and also more medially the trabecular meshwork attaches to it
What separates the anterior and posterior chambers?
The iris
Why is the posterior surface of the iris heavily pigmented in everyone?
To prevent internal light reflection
What is the difference between miosis and mydriasis?
Miosis: parasympathetic, constriction of pupil
Mydriasis: sympathetic, dilation of pupil, much weaker
What is the drainage angle?
Acute angle formed by peripheral iris root and posterior termination of cornea
Contains aqueous outflow apparatus
Most peripheral part of anterior chamber
What are the structures of the drainage angle from anterior to posterior?
Schwalbe’s line
Trabecular meshwork (750 microns wide)
Schlemm’s canal runs externally around it
Juxtacanalicular tissue runs between the outer most part of trabecular meshwork and Schlemm’s canal
Scleral spur
Anterior face of ciliary body
Describe the scleral spur
Wedge shaped ridge of scleral tissue at posterior limit of trabecular meshwork (continuous with outer trabecular beams)
Circular arrangement of collagen and elastic tissue
Deep aspect of sclero-limbal junction
Anterior ciliary muscle inserts into scleral spur from behind
Posterior sheets of outer trabecular meshwork insert into SS from in front
Where is the posterior apex/ border of the drainage angle?
Anterior face of ciliary body
Iris inserts centrally, forming posterior border of drain angle
Where is the internal scleral sulcus?
Circular groove on internal aspect of limbus
Runs from termination of descemet’s membrane to scleral spur
Occupied by the outer portion of TM and SC
What is an iris process?
Present in 1/3 of eyes
Broad based triangular bands that run from iris root to merge with beams of trabecular meshwork
What are the two parts of the trabecular meshwork?
Spongework of connective tissue beams superimposed as perforated sheets
Inner part: uveal meshwork
Outer part: corneo-scleral meshwork
Describe the histology of the uveal meshwork
1-2 innerlayers and 5-6 outer layers of perforated sheets
Intertrabecular spaces 20-75microns
Posteriorly attach to ciliary muscle
Anteriorly taper and attach to Descemets
Describe the histology of the corneoscleral trabecular meshwork
Thicker than inner layer
8-15 layers
Intertrabecular spaces 5-20 microns (smaller gaps)
Anteriorly converges and merges with corneal stroma lamellae
Posteriorly inserts into scleral spur
From inside out, spaces gradually decrease in size, increasing resistance
What are the trabecular beams made of?
Collagenous core surrounded by trabecular cells
How are trabecular cells specialised?
Endothelial-like, line inter-trabecular spaces
Elongated longitudinally, with long cytoplasmic processes
Secretory and phagocytic function
Intracytoplasmic inclusions and pigment seen within cells
What is the cortex of trabecular beams?
PAS +ve basal lamina, attached to trabecular cells
What is in the collagen core of trabecular beams?
Collagen in glycosaminoglycan ground substance
Also some elastin to resume shape after ciliary muscle relaxes
Where is the inner part of the juxtacanalicular connective tissue?
Lies between trabecular meshwork and Schlem’s canal
2-5 loose cells in ECM
10 microns between cells which aqueous drains through
Share basal lamina with endothelium of Schlem’s canal
Cells act to secrete ECM and debris from spaces
Where does the outer part of the juxtacanalicular connective tissue lie and what makes it up?
Lies between Canal of Schlemm and sclera
Less cellular, 4-8 layers of fibrocytic cells
Irregular dense collagen and elastic tissue
Transition zone as collagen lamellae increasingly resemble and merge with overlying sclera
What is the relationship between the canal of Schlemm and the juxtacanalicular connective tissue?
The canal of Schlemm has endothelial lined outpouchings which extend into the jCT to increase the surface area of the canal
The endothelial cells of the canal also sit on an incomplete basal lamina which merges with the adjacent JCT cells
What shape is the canal of Schlemm?
Circular
Ovoid on cross section
What are the two drainage systems of the canal of Schlemm?
Collector channels->drain into venous channels of the angle (no valves so can reflux)
Aqueous veins-> episcleral venous plexus
How many collector channels are there in the canal of Schlemm?
25-35
What is the arterial supply of the drainage angle
Incomplete arterial circle derived from superficial and deep terminal branches of the anterior ciliary arteries
Superficially there are some connections with branches from the vascular plexus in tenon’s fascia and conjunctival vessels at the limbus
Describe the venous drainage of the drainage angle
Canal of Schlemm-> collector channels -> deep scleral venous plexus-> mid scleral venous plexus-> episcleral plexus ->anterior ciliary veins
Which veins drain into the episcleral plexus?
Vortex veins via venous plexus of ciliary body and intrascleral venous network
Aqueous veins
Conjunctival veins
Collector channels via intrascleral venous network at limbus
What is the nerve supply of the drainage angle
Supraciliary nerve plexus and ciliary plexus in region of scleral spur
Myelinated and unmyelinated
Sensory, parasympathetic, and sympathetic innervation
Fibres from nasociliary branch of trigeminal nerve
How does the anterior chamber develop?
Endothelial lined cavity from split in mesenchyme between iris and cornea
1st wave of neural crest mesenchyme forms corneal endothelium anteriorly and 2nd wave forms pupillary membrane posteriorly. Lens moves posteriorly allowing a cavity to form
When does the trabecular meshwork appear?
Differentiates from neural crest mesenchyme at 4 months
By 5 months fenestrations appear in endothelium
When does the ciliary body start producing aqueous?
6th month
Vacuoles are seen
Which embryological tissue forms the canal of schlemm?
Mesodermal mesenchyme
Describe the pathway of flow of aqueous through the drainage angle
Drains through spaces between trabecular beams, then through spaces within JCT
Then transcellularly into canal of Schlemm
Then through collector channels and aqueous veins into venous plexuses
90% of aqueous drains this way
How does the ciliary body affect the aqueous outflow?
When ciliary body contracts it pulls the scleral spur backward which opens intertrabecular spaces and pulls on trabecular meshwork
What is the alternate/uveal scleral drainage pathway?
The anterior portion of the ciliary body extends into drainage angle and the cellular lining of uveal meshwork is incomplete
There is no continuous layer on iris face
Therefore aqueous can gain access across the ciliary body into supraciliary compartment and choroid->suprachoroidal space-> uveal veins
Some diffuses out through sclera
What is the mechanism underlying primary open angle glaucoma?
Increased resistance in trabecular meshwork to outflow
What are some key causes of angle closure glaucoma?
Anatomically narrow angles
Short eyes are prone to angle closure
Dense lens can push forward to close angle (phacomorphic glaucoma)
Intraocular inflammation or neovascularisation can cause scarring of the angle and secondary angle closure
How does the width of the iridocorneal angle change with position?
Widest inferiorly
Narrowest superiorly
What are the three prongs of the sclera at the limbus?
Anterior, middle and scleral spur
Between anterior and middle prongs is cornea
Between middle and scleral spur (internal scleral sulcus) is aqueous drainage apparatus
What occurs in trebeculectomy?
Trabecular meshwork surgically excised to create a fistula between the anterior chamber and the subconjunctival space
