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OPTHT801 > Anterior chamber > Flashcards

Anterior chamber Flashcards

1
Q

What are the borders of the anterior chamber?

A

Corneal endothelium to anterior ciliary body, iris and lens

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2
Q

What is the average depth of anterior chamber?

A

3.15mm

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3
Q

What is the volume of the fluid contained in the anterior chamber?

A

0.2mL

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4
Q

What is the first structure to disappear on gonioscopy if anterior chamber angle narrows?

A

Anterior ciliary body as it just pokes up at the very edge of the angle

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5
Q

Where does the scleral spur run?

A

It runs posterior to the canal of Schlemm and also more medially the trabecular meshwork attaches to it

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6
Q

What separates the anterior and posterior chambers?

A

The iris

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7
Q

Why is the posterior surface of the iris heavily pigmented in everyone?

A

To prevent internal light reflection

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8
Q

What is the difference between miosis and mydriasis?

A

Miosis: parasympathetic, constriction of pupil
Mydriasis: sympathetic, dilation of pupil, much weaker

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9
Q

What is the drainage angle?

A

Acute angle formed by peripheral iris root and posterior termination of cornea
Contains aqueous outflow apparatus
Most peripheral part of anterior chamber

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10
Q

What are the structures of the drainage angle from anterior to posterior?

A

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

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11
Q

Describe the scleral spur

A

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

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12
Q

Where is the posterior apex/ border of the drainage angle?

A

Anterior face of ciliary body

Iris inserts centrally, forming posterior border of drain angle

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13
Q

Where is the internal scleral sulcus?

A

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

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14
Q

What is an iris process?

A

Present in 1/3 of eyes

Broad based triangular bands that run from iris root to merge with beams of trabecular meshwork

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15
Q

What are the two parts of the trabecular meshwork?

A

Spongework of connective tissue beams superimposed as perforated sheets
Inner part: uveal meshwork
Outer part: corneo-scleral meshwork

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16
Q

Describe the histology of the uveal meshwork

A

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

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17
Q

Describe the histology of the corneoscleral trabecular meshwork

A

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

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18
Q

What are the trabecular beams made of?

A

Collagenous core surrounded by trabecular cells

19
Q

How are trabecular cells specialised?

A

Endothelial-like, line inter-trabecular spaces
Elongated longitudinally, with long cytoplasmic processes
Secretory and phagocytic function
Intracytoplasmic inclusions and pigment seen within cells

20
Q

What is the cortex of trabecular beams?

A

PAS +ve basal lamina, attached to trabecular cells

21
Q

What is in the collagen core of trabecular beams?

A

Collagen in glycosaminoglycan ground substance

Also some elastin to resume shape after ciliary muscle relaxes

22
Q

Where is the inner part of the juxtacanalicular connective tissue?

A

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

23
Q

Where does the outer part of the juxtacanalicular connective tissue lie and what makes it up?

A

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

24
Q

What is the relationship between the canal of Schlemm and the juxtacanalicular connective tissue?

A

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

25
Q

What shape is the canal of Schlemm?

A

Circular

Ovoid on cross section

26
Q

What are the two drainage systems of the canal of Schlemm?

A

Collector channels->drain into venous channels of the angle (no valves so can reflux)
Aqueous veins-> episcleral venous plexus

27
Q

How many collector channels are there in the canal of Schlemm?

A

25-35

28
Q

What is the arterial supply of the drainage angle

A

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

29
Q

Describe the venous drainage of the drainage angle

A

Canal of Schlemm-> collector channels -> deep scleral venous plexus-> mid scleral venous plexus-> episcleral plexus ->anterior ciliary veins

30
Q

Which veins drain into the episcleral plexus?

A

Vortex veins via venous plexus of ciliary body and intrascleral venous network
Aqueous veins
Conjunctival veins
Collector channels via intrascleral venous network at limbus

31
Q

What is the nerve supply of the drainage angle

A

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

32
Q

How does the anterior chamber develop?

A

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

33
Q

When does the trabecular meshwork appear?

A

Differentiates from neural crest mesenchyme at 4 months

By 5 months fenestrations appear in endothelium

34
Q

When does the ciliary body start producing aqueous?

A

6th month

Vacuoles are seen

35
Q

Which embryological tissue forms the canal of schlemm?

A

Mesodermal mesenchyme

36
Q

Describe the pathway of flow of aqueous through the drainage angle

A

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

37
Q

How does the ciliary body affect the aqueous outflow?

A

When ciliary body contracts it pulls the scleral spur backward which opens intertrabecular spaces and pulls on trabecular meshwork

38
Q

What is the alternate/uveal scleral drainage pathway?

A

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

39
Q

What is the mechanism underlying primary open angle glaucoma?

A

Increased resistance in trabecular meshwork to outflow

40
Q

What are some key causes of angle closure glaucoma?

A

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

41
Q

How does the width of the iridocorneal angle change with position?

A

Widest inferiorly

Narrowest superiorly

42
Q

What are the three prongs of the sclera at the limbus?

A

Anterior, middle and scleral spur
Between anterior and middle prongs is cornea
Between middle and scleral spur (internal scleral sulcus) is aqueous drainage apparatus

43
Q

What occurs in trebeculectomy?

A

Trabecular meshwork surgically excised to create a fistula between the anterior chamber and the subconjunctival space

OPTHT801 (20 decks)

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