Aqueous Humour & Intraocular Pressure Flashcards
(123 cards)
1
Q
What are the non-sensory and sensory layers of the retina known as?
A
Non-Sensory (Outer)
Sensory (Inner)
2
Q
What does the RPE become?
A
Pigmented layer of the ciliary epithelium
3
Q
Which of the 2 layers of the ciliary epithelium make up the aqueous humour?
A
Non-Pigmented layer
4
Q
Which way do the apexes of the ciliary epithelium layers face?
A
Apexes between the pigmented and on-pigmented layers face each other
5
Q
What is the ciliary body posteriorly continuous with?
A
The Choroid
6
Q
What is the ciliary body posterior to?
A
Peripheral margin of the iris
7
Q
Where does the ciliary body extend?
A
In a complete ring that runs around the inside of the anterior sclera. Extends forward to the scleral spur and backwards to the ora serrata
8
Q
What is the scleral spur?
A
Protrusion of the sclera into the anterior chamber. Seen as a raised bump of the sclera right near the limbus.
9
Q
How is the sclera spur attached?
A
Anteriorly to the trabecular meshwork and posteriorly to the sclera and the longitudinal portion of the ciliary muscle
10
Q
How far does the ciliary body extend?
A
On the outside of the eyeball, the ciliary body extends from a point about 1.5 mm posterior to the corneal limbus to a point 7.5 to 8.0 mm posterior to this on the temporal side and 6.5 to 7.0 mm on the nasal side.
11
Q
Where is the ciliary body located?
A
The ciliary body is triangular on cross-section, with its small base facing the anterior chamber of the eye and its anterior outer angle facing the scleral spur. Its apex extends posteriorly and laterally to become continuous with the choroid.
12
Q
What is the pars plicata?
A
The anterior surface or base of the ciliary body that is ridged/plicated. It surrounds the periphery of the iris and gives rise to the ciliary processes
13
Q
What is the pars plana?
A
The posterior surface of the ciliary body that is smooth and flat.
14
Q
What is the Ora Serrata?
A
The ora serrata is where the retina stops and moves forward to become ciliary non-pigmented epithelium at the point where it thins out. Your pigmented layer continues and doesn’t thin out.
15
Q
Which layer of the ciliary epithelium thins out?
A
The non-pigmented layer
16
Q
Which of the ciliary epithelium layers is more inner?
A
The non-pigmented layer
17
Q
Which of the ciliary epithelium layers is more outer?
A
The pigmented layer
18
Q
What type of cells cover the inner surface of the ciliary body?
A
The ciliary epithelium consists of two layers (pigmented and non-pigmented) of cubical cells
19
Q
What is the non-pigmented layer an extension/continuation of?
A
Anterior extension of the neural retina. Specifically of the inner limiting membrane. These cells are also line the anterior chamber. They secrete aqueous humour.
20
Q
What is a continuation/extension of the retina’s RPE?
A
The pigmented outer layer of the ciliary epithelium. They rest against the ciliary stroma which is made up of loose connective tissue.
21
Q
What borders the basement membrane of non-pigmented layers?
A
The basement membrane of the non-pigmented cells faces the posterior chamber and is continuous with the inner limiting membrane of the nervous part of the retina.
22
Q
What borders the pigmented layer of the ciliary processes?
A
The basement membrane of the pigmented cells faces the stroma and is an extension of the basement membrane of the pigmented epithelium of the retina (RPE)
23
Q
How vascular is the ciliary body?
A
The ciliary body is incredibly vascular. Per area of weight of the EOM they’re the most vascular muscles of the body and the ciliary body follows just behind this.
24
Q
What type of muscle makes up the ciliary muscle?
A
Smooth muscle fibres
25
Where are most of the muscle fibres of the ciliary muscle attached?
To the scleral spur
26
What the the 3 main groups of muscle fibres of the ciliary body?
1) Longitudinal Fibres
2) Oblique/Radial Fibres
3) Circular Fibres
27
Where are Longitudinal fibres of the ciliary muscle located?
The longitudinal fibers- the most external and closest to the sclera-pass posteriorly into the stroma of the choroid.
28
Where are Oblique/Radial fibres of the ciliary muscle located?
The oblique/radial fibers (around in a ring of the ciliary body) run from the first layer to the third layer and radiate out from the scleral spur.
29
Where are the Circular Fibres of the ciliary body located?
The most internal. Run around the eyeball like a sphincter. They lie close to the peripheral edge of the lens.
30
What pulls the ciliary body forward in accommodation?
It is the contraction of the ciliary muscle, especially the longitudinal and the circular fibers, that pulls the ciliary body forward in accommodation. This forward movement is responsible for relieving the tension in the suspensory ligament, making the elastic lens more convex and thereby increasing the refractive power of the lens.
31
What nerve innervates the ciliary body?
The nerve that innervates the ciliary body are the post-ganglionic parasympathetic fibres of the oculo-motor nerve. The nerve fibres reach the muscle via the short ciliary nerves.
32
Define the aqueous humour
The clear fluid which fills the anterior and posterior chambers of the eyeball.
33
What are the 3 functions of aqueous humour?
- Source of nutrients for avascular tissues in the anterior chamber
- Removes waste products from structures in the anterior chamber
- Maintains IOP (intraocular pressure)
34
What avascular tissues does the aqueous humour provide nutrients too?
It is the source of nutrients for the avascular tissues of the anterior chamber, including the cornea and lens, and it removes their waste products.
35
How does the aqueous humour maintain intraocular pressure?
Aqueous controlled circulation around the AC and out through the anterior chamber angle (trabecular meshwork) is necessary for IOP maintenance
36
Where do the lens and cornea get their nutrients from?
Lens & endothelium of the cornea = avascular so can’t get oxygen and nutrients from blood so have to get it from aqueous humour that nutrients to avascular structures in the anterior chamber.
37
What is it called when blood gets into the aqueous humour?
Hyphema which is usually caused by a puncture of the globe or of the ciliary muscle.
38
What is it called when pus gets into the aqueous humour?
Pus can get into the anterior chamber into the aqueous humour (hypopyon) which is usually from an ulcer from the eye.
39
Where is aqueous humour produced?
Generated by the posterior chamber of the eye by the ciliary processes
40
Why is stromal fluid similar chemically to blood plasma?
The capillaries in the stroma of the ciliary processes are highly permeable and so stromal fluid is very similar chemically to blood plasma.
41
What forms the blood-aqueous barrier?
The pigmented and non-pigmented layers of the ciliary epithelium have intercellular gap junctions between them and are what form the blood-aqueous barrier. Blood aqueous barrier is formed by a structure called the zonula occludens which resides in the nonpigmented ciliary epithelium layer. It prevents blood from mixing with the AqH. In inflammatory processes, it can become disrupted
42
How does secretion of stromal fluid from the capillaries work?
Through active transport and through capillary fenestrations (ultrafiltration aka holes in the capillaries)
43
How much aqueous fluid is produced per minute?
3 micromillitres per minute
44
What ions are involved in the production of aqueous fluid?
The major ions involved in this process are Na+, HCO3−, and Cl−. The osmotic pressure in the intercellular clefts increases as ions are pumped in. Water and its solutes follow and eventually move out of the clefts and into the posterior chamber. Enzymatic inhibitors of these transport processes significantly reduce aqueous flow.
45
What is the process of aqueous humour getting from capillary to aqueous humour?
Some products (sodium na+, hydrogren bicarb HCO3-, chloride cl- and accurbic acid) leave the capillary at this point. These are squeezed out of the blood to the connective tissue and moves towards the double layer of the epithelium. The epithelium uses active transport proteins to push sodium out of the epithelium. This is followed by chloride and bicarb that leave also (leave blood supply in the ciliary process) which increases oncotic pressure which, when this happens water will follow this also as they can move with the negative ions leaving. It changes into aqueous humour by the non-pigmented layer which then enters the posterior chamber and it is then drained and contributes to intraocular pressure.
46
What is the rhythm of aqueous humour like?
Circadian Rhythm that maintains a predictable pattern of IOP (inflow and outflow) throughout a 24 hour period
47
What does persistent elevation of IOP cause?
Increase in the risk of glaucoma (want to treat by decreasing aqueous humour production)
48
What does chronically low IOP (hypotony) cause?
Increase risk of sight-threatening conditions including corneal changes, accelerated cataract formation, choroidal fluid, maculopathy, cystoid macular edema, or optic disk edema. IOP has to be less than or equal to 5mmHg on 3 different measurements
49
What control is the circadian rhythm of aqueous humour under?
It is thought to follow circadian changes in autonomic tone and circulating corticosteroids suggesting ciliary processes are under autonomic control.
50
What are Alpha adrenergic agonists for?
Adrenergic Agonists increase aqueous humour production - During the day, when background autonomic tone is relatively high and aqueous humor is being produced at a relatively fast rate, α2 adrenergic agonists and β-blockers effectively reduce aqueous flow and IOP.
51
What are Beta adrenergic agonists for?
Beta Adrenergic Agonists tend to decrease aqueous humour production - at night when adrenergic tone is relatively low and aqueous humor is being produced at about half its daytime rate, α1adrenergic agonists and β-blockers have little effect on aqueous flow and IOP
52
What is reduction of aqueous humour formation as we age accompanied by?
A reduction in the volume of the anterior chamber by approx 14 - 24 micromillitres per decade. This means the smaller anterior chamber requires less flow to maintain the same clearance.
53
How much does aqueous humour and anterior chamber volumes decrease by as we age?
From age 20 to 80 years, aqueous humor flow rate decreases by approximately 25%, while anterior chamber volume decreases by 40%, and this combined change provides a 20% faster turnover rate of aqueous humor over a lifetime.
54
What are the major components of aqueous humour?
- Various ions
- Carbohydrates
- Proteins
- Oxygen
- Carbon dioxide
- Water
- Urea
- Glutathione
55
What are important anti-oxidant substances in the aqueous humour?
Important anti-oxidant substances can also be found in the aqueous humour, such as glutathione (derived by diffusion from the blood) and ascorbate (which helps protect against light-induced oxidative damage).
56
Is there any difference between the fluid in the posterior and anterior chambers and if yes, what?
No differences
57
What is higher and what's lower in aqueous humour than in blood plasma?
Ascorbate is higher in aqueous humour than the blood serum/plasma yet protein concentration, glucose and urea is lower.
58
What is the Canal of Schlemm/Schlemm's Canal?
Goes around the limbus, 25-27 valves that the aqueous humour enters via the venous network which is the scleral-aqueous network.
59
Where is Schlemm's Canal?
It’s at the Iridio-corneal angle (basically where the limbus is) found in the posterior part of the corneoscleral junction
60
What's another name for Schlemm's canal?
Scleral Venous Sinus
61
What is the function of Schlemm's canal?
The function of Schlemm’s canal is to collect the aqueous humour from the anterior chamber of the eyeball and deliver it to the veins of the eyeball.
62
How does the aqueous humour leave the eye via passive flow?
Via two pathways at the anterior chamber angle anatomically located at the limbus called the conventional and non-conventional pathways
63
What is the route of aqueous humour through the conventional pathway/pathway 1?
Secretes aqueous humour via non-pigmented layer, Posterior Chamber, flows over the lens and gives it a wash, then meets distal iris and fills the anterior chamber (in utero) and then when full, drains out the trabecular meshwork and behind that is Schlemm’s canal, into its lumen and into draining collector channels, aqueous veins and episcleral veins.
64
What % of aqueous humour leaves via the conventional pathway?
80-90%
65
How does the conventional pathway allow movement of aqueous humour?
It occurs down a pressure gradient from the trabecular meshwork into Schlemm’s canal and through it’s inner wall.
66
What is the rate limiting step in pathway 1?
Canal of Schlemm
67
How does aqueous humour in the the non-conventional route travel?
The non-conventional route is composed of the uveal meshwork and anterior face of the ciliary muscle. The aqueous humour enters the connective tissue between the muscle bundles, through the suprachoroidal space, and out through the sclera. We don't know exactly how this route works.
68
What is the rate limiting step in pathway 2?
Flow through the ciliary muscle by how thick it is
69
What is the trabecular meshwork made up of?
Made up of 3 sections of very fine connective tissue with mini canals going through them to support the TM
69
What is the function of the trabecular meshwork cells?
- Maintain passageway patency by producing antithrombotic agents
- Neutralize oxidative species
- Phagocytes
- Biological filter
- Immune mediation
- Connective tissue turnover and repair
70
What are the three consecutive regions of the trabecular meshwork?
Uveal meshwork, corneoscleral meshwork and the juxtacanalicular region
71
Which section of the trabecular meshwork is the most inner layer?
Uveal meshwork is closest to the iridio-corneal angle and thus is what the aqueous first meets
72
Describe the uveal meshwork
- Innermost layer
- What the aqueous first meets
- Consists of approx 3 layers of connective tissue beams
- Covered by flat, confluent TM cells with irregular fenestrations
73
Describe the Corneoscleral Meshwork
- Where the cornea meets sclera
- 8-15 layers of perforated sheets of fibres or beams
- Covered by TM cells
- Intrabecular spaces become smaller as they extend closer to Schlemm's Canal
74
Describe the Juxtacanalicular tissue
- Outermost layer
- Contains Stellate (star) shaped cells (NOT TM cells)
- Connect to the endothelial cells of the canal
- 2-5 layers
- Thinnest
- Responsible for most of the resistance in outflow
75
Why does the trabecular meshwork have layers?
Allows us to change the rate at which the aqueous humour passes through these holes. We have trabecular meshwork cells that allow us to change the rate at which fluid passes through the trabecular meshwork i.e. if heart rate increases with increased amount of fluid coming through, they do things to slow down the aqueous humour passing through the eye to make them more permeable to fluid passing through (the canals also generally slow the fluid)!
76
Where are TM cells located?
In the Uveal and Corneoscleral trabecular meshwork layers
77
Why do we have TM cells?
They act as aggressive phagocytes, removing cellular debris from the AqH before it reaches the final layer. Act as phagocytes so get rid of any bacteria that shouldn’t be entering the venous system. So TM cells have an element of anti-microorganism filter and can change immuno-competency of the aqueous humour
78
What is a normal IOP?
10 - 21mmHG (average is 15)
79
How can IOP fluctuate?
- Exercise
- Heart rate
- Trauma
- Fluid Intake
- Medications
- Body orientation
- Alcohol and recreational drugs
80
What responds to fluctuations in IOP?
TM cells respond to adjust outflow resistance (mount a homeostatic response to restore IOP within normal range). They make it harder for easier for fluid to pass through.
81
What type of secretion produces aqueous humour?
It is produced predominantly by active secretion (90%) in the non-pigmented epithelium of the pars plicata of the ciliary body.
82
What maintains transparency and immune privilege of the aqueous?
The blood-aqueous barrier
83
What is Glaucoma?
An umbrella term for diseases which increase IOP resulting in irreversible but potential preventable vision loss, via damage to the optic nerve
84
What terms can be used to describe glaucoma?
Primary Open Angle Glaucoma (POAG)
Secondary Open Angle Glaucoma (POAG)
Primary Angle Closure Glaucoma (PACG)
Secondary Angle Closure Glaucoma (SACG)
Congenital
Juvenile
85
What is open-angle glaucoma also known as?
Just glaucoma
86
What is primary open angle glaucoma?
Resistance in the TM
87
What is secondary open angle glaucoma?
Resistance in the TM due to an underlying problem which can be identified and if corrected, then theoretically the glaucoma would resolve
88
What is primary angle closure glaucoma?
Acute blockage of drainage systems due to peripheral iris obstructing TM (pupil block) > optic nerve damage. If the optic nerve has not yet been damaged then it is called primary angle closure.
In primary angle-closure there is a pupil block where the distal iris will touch and adhere to the lens meaning that any fluid in the posterior chamber comes out into the anterior chamber and intraocular pressure starts to rise.
89
What is Secondary angle closure glaucoma?
Due to other conditions which either push or pull the iris forward to contact the TM
90
What is the annoying type of glaucoma?
Annoyingly there is also a normal tension/pressure glaucoma where patients have the same visual loss pattern as POAG but with normal IOP.
91
What causes Open Angle Glaucoma (either primary or secondary)? What about in Closed-Angle?
Increased resistance in the TM which increases IOP.
In primary angle-closure there is a pupil block where the distal iris will touch and adhere to the lens meaning that any fluid in the posterior chamber comes out into the anterior chamber and intraocular pressure starts to rise. Leave untreated the cornea will get condensed and so the excess aqueous humour will go behind the lens. This will affect the optic nerve the most as it gets condensed/pressed as there is already vitreous in here. The central retinal artery travels through the middle of optic nerve and splits into superior and inferior artery so blood supply to the eye cuts off causing the retina to become hypoxic and cause it to die (retina can live 90 minutes without blood). Need to take medication.
In primary closed angle glaucoma the same pathology has happened, more time has passed, and the raised intraocular pressure has caused damage to the optic nerve resulting in changes to vision. As the aqueous humour builds in the posterior chamber the peripheral iris starts to bulge forward which occludes the TM. Longer you leave it, the worse you are. Bows the iris and the iris attaches to the lens which causes “pupil block” leading to mid-dilated eyes (as they cannot dilate further or constrict further).
92
What happens to the central retinal artery in primary angle-closure glaucoma?
The central retinal artery travels through the middle of optic nerve and splits into superior and inferior artery so blood supply to the eye cuts off causing the retina to become hypoxic and cause it to die (retina can live 90 minutes without blood).
93
What drug do you give someone with close angle glaucoma?
Pilocarpine - is a miotic and is used to straighten out the iris to open up the trabecular meshwork. This stops pressure from getting horrendous as reduces IOP but still need further treatment. If you put them in a dim room it makes it so much worse because the pupil dilates and the iris gets bunched.
94
What drug is used to reduce aqueous humour production?
Acetazolamide is used to reduced aqueous humour production by reducing CSF production that also stops the aqueous humour production
95
What's an Iridotomy?
We would poke a new hole to create a new trabecular meshwork through an Iridotomy to laser a hole in the iris. To create a permanent channel near the trabecular meshwork.
96
What is an iridectomy?
Iridectomy to cut a rectangle of the iris out of the eye (surgery) to stop an acute angle closure from ever happening again (if the pressure isn’t too high).
97
What happens to be cornea with increased IOP?
If pressure if too high then aqueous humour gets through the layers of the cornea OR compresses the layers due to the IOP.
98
What type of visual loss does glaucoma result in?
Will get peripheral VF loss due to the nerve being squished outside in (outside tend to be for peripheral vision and inside for central vision)
99
What are the symptoms and signs of primary acute closure angle glaucoma (PACG)?
- Severe, sudden ocular pain
- Red eye (because the eye is under pressure so vessels get grossly distended)
- Reduced vision (cornea’s stroma gets squashed so becomes hazy or the optic nerve gets affected, longer you leave it the more the VA gets affected)
- Decreased VA
- Headache
- Nausea / vomiting (head pressure getting higher)
- Halos of light
100
What are the signs on examination of primary acute closure angle glaucoma (PACG)?
- Unresponsive dilated pupil (unless very early caught)
- Firm eyeball (like pebble under the eye)
- High IOP (30-50)
- Large optic cup
101
What are the symptoms of primary open angle glaucoma?
- Can be asymptomatic
- Peripheral vision loss (Arcuate scotoma on visual field testing)
- Large optic cup (dip in cup gets bigger so pushes out so causes a large cup-disc ratio; fewer nerves course through optic disc)
- Raised IOP (unless NTG)
- Vertical thinning and notching of neural rim (space between inner cup and surrounding disc)
- Optic atrophy - optic disc becomes pale as damage progresses
102
What medical treatments are there for glaucoma management?
- Prostaglandin analogues
- Beta Blockers
- Carbonic anhydrase inhibitors
- Alpha 2 Agonists
- Miotics
103
What surgical treatments are there for glaucoma?
- Laser trabeculoplasty
- Trabeculectomy
- Shunt insertion
- PCAG – laser iridotomy
104
What are the aims of glaucoma management?
Glaucoma management is tailored to the specific type and severity. However, there is no treatment at this time that can reverse any of the vision loss that has occurred, it can only help to prevent further damage and vision loss. Visual field testing and mapping of vision loss are helpful in monitoring disease progression.
105
How is open-angle glaucoma generally managed?
Initially with medications to lower eye pressure
106
What is laser trabeculoplasty?
Laser trabeculoplasty is also used as a primary treatment option in some cases. If medical management cannot be achieved successfully, procedures like laser trabeculoplasty, trabeculectomy, inserting a drainage valve/tube shunt, or laser treatment to the ciliary body to reduce aqueous production can be used to establish better control of IOP.
107
What is Minimally Invasive Glaucoma Surgery (MIGS)?
Minimally invasive glaucoma surgery (MIGS) is another evolving option for those who have mild-moderate glaucoma. MIGS has a more favourable overall safety profile compared with conventional trabeculectomy and tube shunts, more rapid recovery time, and has proven effective for IOP reduction to the mid-high teens level. Studies also support that MIGS placement can reduce the number of pressure-lowering medications required to maintain target IOP levels.
108
How does laser work in glaucoma?
Patients can take medication to reduce eye pressure as quickly as possible but usually require a laser procedure called laser peripheral iridotomy. This laser creates a small hole in the iris to relieve the pupillary block, causing the pressure gradient between the posterior and anterior chambers to equalize, resolving iris bombe and opening the anterior chamber drainage angle.
The peripheral iris can be flattened with laser iridoplasty and, less commonly, with laser pupilloplasty.
109
Is decreased intraocular pressure confirmation that the angle has reopened in glaucoma?
Decreased intraocular pressure is not necessarily a confirmation that the angle has reopened since the ciliary body can undergo ischemic damage during an attack and have decreased production for a few weeks, so it is important to have a follow-up gonioscopy to ensure the angle has reopened and to comment on the percentage of the angle with peripheral anterior synechia from the acute or prior subacute attacks
110
What is Ocular Hypotony?
A potentially vision threatening condition where IOP falls (<5mmHg) resulting in loss of structural stability of the globe
111
What can cause ocular hypotony?
Acute
- Trauma
- Post surgery
Chronic
- Medication use
- Chronic health problems
112
What is the pathology of ocular hypotony?
- Not enough formation of AqH or
excessive loss of AqH
- AP length of the eyeball shortens so sclera buckles
- Macula and retina affected
- Optic nerve affected (Optic nerve becomes affected because the lamina cribrosa (where the vessels and oN pass through), bows anteriorly)
- Vision affected
113
Is Aqueous Humour a passive or active process?
Active
114
What's not involved in the process of aqueous humour?
Ultrafiltration
Active transport (at the membrane)
Diffusion (through the stroma)
Reverse Osmosis
Reverse Osmosis
115
What is Vitamin C also known as?
Ascorbic Acid
116
Where is the base of the ciliary body?
Towards the iris
117
Where is the apex of the ciliary body?
Towards the Ora Serrata
118
Basal lamina (BASE) of non-pigmented epithelium is in direct contact with what?
Aqueous Humour
119
What is at the apex of the non-pigmented epithelium against?
Apex of non-pigmented epithelium is the BASE membrane of pigmented epithelium
120
What happens to the shape of cells as they approach the pars plicata?
They become more columnar than cubic as they approach the pars plicata
121
The anterior origin of the ciliary musculature is what?
Scleral Spur
122
