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Aqueous Humor Production Flashcards

1
Q

Fonctions de l’humeur aqueuse (x4)

A
  1. Supply nutrients (O2, glucose, AA, etc.) to avascular and transparent optical structures (lens, cornea), trabecular meshwork and cornea
  2. Remove waste (lactic acid, CO, etc.)
  3. Create positive IOP : structural integrity of eye
  4. Clear debris in pathologic conditions : facilitates cellular and humoral immune responses, decreased formation during inflammation to permit accumulation of immune mediators
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2
Q

Où est produite l’humeur aqueuse

A

Surface of ciliary processes (pars plicate of ciliary body region)

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3
Q

Vrai ou Faux : Le corps ciliaire est composé de 70-80 major processes?

A

Vrai

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4
Q

La shape du corps ciliaire est-elle régulière ou irrégulière? Et pourquoi?

A

Irregular shape
Allows for larger surface area for production of fluid (total : env. 6 cm^2)

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5
Q

Vrai ou Faux : Vascularized inter core (du corps ciliaire) with low perfusion rate surrounded by loose tissue stroma.

A

Faux. Vascularized inter core with VERY HIGH perfusion rate surrounded by loose tissue stroma.

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6
Q

Comment sont les capillaires dans le corps ciliaire?

A

Fenestrated capillaries highly permeable to water & plasma

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7
Q

Caractéristiques de l’épithélium des processus ciliaires?

A

Double epithelium layer :

  1. Inner NON-pigmented : outer side of the processes, continuation of retina
  2. Outer PIGMENTED : on the inner side of the processes, continuation of RPE
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8
Q

Que sont les « zonula occludens » et dans quel épithélium des processus ciliaires sont-ils situés?

A

Tight junctions of the NON-pigmented epithelium impermeable to water forms BLOOD-AQUEOUS BARRIER. Si disruption of barrier : cell & flare in AC.

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9
Q

Quel est le vascular supply du corps ciliaire?

A

MAJORITY of blood supply :
2 LONG posterior ciliary arteries : a. ophtalmique → 2 long posterior ciliary arteries → major arterial circle

SMALLER portion of blood supply to major arterial circle :
7 branches of anterior ciliary arteries

Very high perfusion rate (env. 150 mL/min)

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10
Q

Vrai ou Faux : Le corps ciliaire a un low perfusion rate?

A

Faux. Very high perfusion rate (env. 150 mL/min)

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11
Q

Quelles structures forment le BLOOD AQUEOUS Barrier du corps ciliaire?

A

Les Zonula occludens (ZO) form tight junctions in NON-pigmented epithelium, forming the blood-aqueous barrier at the ciliary body

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12
Q

Que se passe-t-il si disruption du blood aqueous barrier?

A

Cell & flare in AC

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13
Q

Mechanisms of Aqueous Secretion (x3)

A
  1. Ultrafiltration
  2. Diffusion
  3. Active transport
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14
Q

Quelles sont les caractéristiques de l’ultrafiltration?

A

Pressure difference between ciliary process stroma and post chamber

Transports small, WATER-soluble molecules

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15
Q

Quelles sont les caractéristiques de la diffusion?

A

From high to low concentration
Ciliary process stroma → post chamber

Transports LIPID-soluble molecules

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16
Q

Quelles sont les caractéristiques du transport actif?

A

Most important mechanism (> 80% of total production)

Na/K/ATPase pump

Transports Na, HCO3, Cl, water, large WATER-soluble molecules

Tx inhibiteurs de l’AC : diminue HCO3, nécessaire pour transport actif du Na = inhibition du transport actif

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17
Q

Quelle est la [ ] de protéines dans l’humeur aqueuse (faible ou élevée)? Et pourquoi?

A

Very low protein concentration
Allow for optical clarity of fluid
Mostly albumin and globulin

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18
Q

Composition de l’humeur aqueuse (x5)

A

Very low protein [ ]
High in H+ et Cl
High [ ] of ascorbic acid and lactate
O2
HCO3

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19
Q

Quel est l’average moyen du taux de production de l’humeur aqueuse?

A

Average daily 2,4 ul/min

20
Q

À quel moment de la journée la PIO est-elle le plus élevée?

A

HIGHEST Overnight > Morning > Afternoon > Nocturnal

Highest overnight à cause de la diminution du retour sanguin au coeur en DL

21
Q

Concernant l’HA, Augmentation ou diminution :
1. Production avec l’âge?
2. Incidence du POAG avec l’âge?

A
  1. Decreased production with age (2% per decade)
  2. POAG incidence increases with age

Evidence suggestif that high IOP observed in glaucoma NOT due to aqueous overproduction as there is a negative correlation between
- Aqueous overproduction and IOP fluctuation throughout the day
- Incidence of the disease increases with age while the rate of aqueous production is decreasing with age

22
Q

Facteurs augmentant aqueous formation (x3)

A

Hyperthermie
Alcalose
Conditions hypo-osmotiques

23
Q

Facteurs diminuant aqueous formation (x6)

A

Hypothermie
Acidose
Conditions hyper-osmotiques
Ocular pathology : Db, R/D, cyclo-dialysis, uveitis
Systemic pathology : carotid occlusive disease
Rx : BB, CAI’s, alpha-agonists

24
Q

Quels sont les deux outflow pathways?

A

Conventional (90%)
Unconventional/Uveoscleral (10%)

25
Q

Trajet du conventionnel outflow pathway

A
  1. AC
  2. Trabecular meshwork (TM)
  3. Juxtacanalicular tissue
  4. Schlemm’s Canal
  5. Collector channels
  6. Aqueous veins
26
Q

Quelles sont les 3 layers du trabecular meshwork?

A
  1. Uveal Meshwork (next to AC)
  2. Corneoscleral Meshwork
  3. Juxtacanalicular Tissue (next to Scheme’s canal)
27
Q

Où se situe la majorité du outflow resistance (50 à 90%)?

A

Trabecular meshwork
- Site of elevated outflow resistance in glaucoma

28
Q

Fonctions d’un high outflow résistance dans le trabecular meshwork?

A

Resident population for phagocytosis of debris carried into TM by aqueous

One-way valve permits fluid to leave eye but restricts retrograde flow (of blood, proteins…) = critical part of normal blood-aqueous barrier

29
Q

Qu’est-ce que la ligne de Schwalbe?

A

Zone de transition from trabecular to corneal endothelium : termination of Descemet’s membrane and insertion of trabecular meshwork into corneal stroma

30
Q

Fonctions du corneoscleral meshwork (x3)

A

Avidly phagocytic : clear out aqueous debris
Maintain extracellular matrix (ECM) composition : mechanical structure to meshwork
Control ECM : important determinant of outflow resistance

31
Q

Vrai ou Faux : le juxtacanalicular tissue is a major site of outflow resistance.

32
Q

Vrai ou Faux : le canal de Schlemm est un major site of outflow resistance.

A

Faux. Small % of total outflow resistance.

33
Q

Vrai ou Faux : le size des canal varie selon la PIO.

A

Vrai.
Augmentation PIO : canal collapses while TM expands.

34
Q

Combien y a-t-il de canaux collecteurs après le canal de Schlemm?

A

Environ 30

35
Q

Dans quelle structure vasculaire l’humeur aqueuse est-elle drainée éventuellement?

A

Sinus caverneux

36
Q

Les canaux collecteurs s’anastomosent à quels vx?

A

Aqueous veins puis episcleral venous system

37
Q

Fonctionnement du oveoscleral outflow.

A

Passage of fluid from AC into iris root, anterior face of ciliary muscle, between the muscle fibres, and finally into the suprachoroidal space

38
Q

Vrai ou Faux: Les analogues des prostaglandines augmentent uveoscleral outflow.

39
Q

Vrai ou Faux : l’uveoscleral outflow diminue avec la cycloplégie.

A

Faux. Increased with cycloplegia.

40
Q

Factors affecting outflow facility (x5)

A
  1. Decreased with age
  2. Decreased with corticosteroids
  3. Increased with ciliary muscle tone (accommodation, pilocarpine)
  4. Increased in Surgery (trabeculoplastie, canaloplastie, canal stents)
  5. Decreased in Glaucoma (primaire et secondaire)
41
Q

Why does the eye need positive IOP? (x2)

A

To maintain shape of structure
To maintain flow of nutrients

42
Q

Moyenne générale dans la population de la PIO?

A

15,5 +/- 2,6 mmHg

N : 12-21mmHg

Anormale : > 2 écart-types (22 mmHg)

43
Q

La distribution de la PIO chez la population est-elle Gaussian?

A

Gaussain : young (20-40 ans)
Non-Gaussain tail at higher (> 40 ans)

44
Q

Facteurs déterminant la PIO (aka Goldmann equation)

A

IOP = EVP + FLOW/(Cuveo + Cconv)

EVP : pression veineuse épisclère
IN : flow
OUT : Cuveo et Cconv

45
Q

Impact des caractéristiques suivantes sur la PIO :
- Age
- Noirs
- HTA
- Hx fam de glaucome
- High myopes (> -6D)
- Db
- Posture : supine versus head down
- Exercice : aigu versus prolongé
- Variation diurne
- Symétrie

A
  • Age : augmente
  • Noirs : higher
  • HTA : augmente
  • Hx fam de glaucome : higher
  • High myopes (> -6D) : higher
  • Db : higher
  • Supine position : augmente légèrement (1-6 mmHg)
  • Head down : augmente davantage (16 mmHg)
  • Exercice aigu : augmente
  • Exercice prolongé : diminue
  • Variation diurne : Nuit > Matin > PM. Si variation diurne > 7 mmHg = ANORMALE
  • Symétrie : Si asymétrie > 5 mmHg = ANORMALE
46
Q

Sources of Error in Goldmann Tomometry

A

Cornea’s thickness
-Thick : Overestimate
- Thin : Underestimate

Greater-than-normal corneal curvature : Overestimate (1 mmHg for each 3D corneal P)

Astigmatism > 3D : Over ou Underestimate depending on the type of astigmatism (axis)

Fluorescein on cornea :
- Too much : Overestimate
- Not enough : Underestimate

Finger pressure on the lid or globe : Overestimate

Patient breath holding : Overestimate

Patient’s collar (cravate) : Overestimate

Corneal scarring

47
Q

3 façons de réduire la PIO

A

Reducing aqueous production (inflow) : CAI’s, BB, alpha-agonist

Increased uveoscleral outflow : analogues PG

Increased conventional outflow : pilocarpine

TORIC (17 decks)

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