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TORIC > Corneal anatomy > Flashcards

Corneal anatomy Flashcards

1
Q

Quels sont les différentes layers de la cornées

A

Épithélium
Bowman’s membrane
Stroma
Descemet’s membrane
Endothélium

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2
Q

Quels sont les dimensions de la cornée?

A

Elliptical anterior surface : 11 x 12 mm

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3
Q

Quelle est l’épaisseur de la cornée?

A

Central thickness : 520 microns (moyenne)
Peripheral thickness : 1000 microns

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4
Q

Lequel est FAUX concernant la cornée.
1. Transparente
2. Avasculaire
3. Thickness diminue avec l’âge

A

Réponse : 3
Thickness INCREASES with age

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5
Q

Lequels sont FAUX concernant la cornée.
1. Central cornea is steeper (plus courbée) than periphery
2. After MYOPIC refractive surgery (PRK, LASIK), the central cornea becomes steeper
3. After HYPEROPIC refractive surgery the central cornea becomes flatter
4. Keratometer measures the central 3.6 mm of the cornea
5. Computerized topography measures thousands of curvature points on the cornea

A
  1. VRAI : Central cornea is steeper (plus courbée) than periphery
  2. FAUX : After MYOPIC refractive surgery (PRK, LASIK), the central cornea becomes FLATTER
  3. FAUX : After HYPEROPIC refractive surgery the central cornea becomes STEEPER
  4. VRAI : Keratometer measures the central 3.6 mm of the cornea
  5. VRAI : Computerized topography measures thousands of curvature points on the cornea
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6
Q

Évolution de la courbature avec l’âge?
Infancy versus Middle age

A

Curvature changes with aging
More spherical in infancy
With-the rule astigmatism in chilhood and adolescence
More spherical in middle age
Against-the-rule astigmatism in the elderly

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7
Q

Tissue Removal dans le LASIK et PRK

A

Human hair : 50 um
-1D = 16 um
-3D = 46 um
-8D = 113 um
+1D = 16 um
+3D = 46 um

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8
Q

Fonctions de l’épithélium cornéale (x3)

A

Mechanical barrier to microorganisms
Maintenance of barrier to diffusion of water & solutes
Creation of a smooth, transparent optical surface

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9
Q

Vrai ou Faux : continuous migration of epithelial cells from basal surface toward the tear film where they slough (muent).

A

VRAI

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10
Q

Quel est le turn over de l’épithélium cornéen?

A

Corneal epithelium turns over about ONCE A WEEK

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11
Q
  1. Nombre de cell layers a/n épithélium cornéen
  2. Les ¢ de l’épithélium cornéen sont-elle kératinisées?
A

5-7 cell layers
3 cell types
NOT keratinized
Strong barrier
Zonale occludens permettant tight junctions

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12
Q

Vrai ou Faux : les inner cell membranes of epithelial cells show microvilli

A

FAUX : OUTER cell membrane of epithelial cells show fingerlike projections known as microvilli

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13
Q

À quoi servent les microvilli a/n de l’épithélium cornéen?

A

Microvilli trap tear fluid and prevent drying of the epithelial cells

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14
Q

La membrane basale est-elle dans l’épithélium cornéen ou a/n de la Bowmans Layer?

A

Corneal epithelium
Basal cells are attached to underlying basement membrane (BM)
If BM is damaged, it can be regenerated by the epithelium

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15
Q

Exemples d’anomalies de la membrane basale de l’épithélium cornéen (x3)

A

Recurrent corneal erosions
Epithelial BM dystrophy (EBDM)
Db

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16
Q

2 exemples de pseudokératocone à la kératométrie

A

Epithelial BM dystrophy (EBDM)
SPK

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17
Q

2 principaux métabolismes de l’épithélium cornéen

A

Store large quantities of glycogen

Glycogen can be converted to glucose

Glucose can be metabolized through KREB CYCLE or HEXOMONOPHOSPHATE SHUNT to provide energy for metabolic functions

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18
Q

Conséquence d’hypoxic conditions (ex. tightly fitted contact lens) a/n de l’épithélium cornéen

A

Hypoxic conditions → Acide lactique → OEDÈME ÉPITHÉLIAL

19
Q

Fonctions Bowmans Layer et Stroma (x3)

A

TRANSPARENCY so as to allow the transmission of light

Maintain a FIXED SHAPE so that the cornea can function optically

PROTECTION of the intraoculor contents

20
Q

Vrai ou Faux : Bowman’s layer est une membrane basale

A

FAUX : Bowman’s layer is NOT a true membrane. It is condensation of collagen fibrils of the stroma.

21
Q

Lequel est FAUX concernant le stroma

  1. 30% of corneal thickness
  2. Consist of collagen fibrils, ground substance and keratocytes
  3. Bundles of collagen fibres constitute lamellae
  4. Ground substance : keratin sulfate, chondroitin sulfate
  5. Keratocytes synthesize collagen & mucoprotein
A
  1. FAUX : 90% of corneal thickness
  2. VRAI : Consist of collagen fibrils, ground substance and keratocytes
  3. VRAI : Bundles of collagen fibres constitute lamellae
  4. VRAI : Ground substance : keratin sulfate, chondroitin sulfate
  5. VRAI : Keratocytes synthesize collagen & mucoprotein
22
Q

De quoi est composé le stroma?

A

Collagen fibrils
Ground subtance
Keratocytes

23
Q

Que synthétisent les kératocytes du stroma?

A

Collagène
Mucoprotéine

24
Q

Pourquoi la cornée est-elle transparente

A

Because of small diameter of collagen fibrils and the narrow separation between the fibrils

25
Q

Qu’est-ce que le Corneal Collagen Cross-linking?

A

Corneal Collagen Cross-linking (CXL) is a minimally invasive procedure used to prevent progression of corneal ECTASIA (ex. keratoconus, post-LASIK ectasia)
Ectasie : déformation cornée

Cross-linking of the collagen refers to the ability to form strong chemical bonds with adjacent fibrils.
In the cornea, collagen cross-liking occurs naturally with aging due to an oxidative deamination reaction.

26
Q

Quel est le Tx du Corneal Collagen Cross-linking (CXL)?

A

Riboflavin 0,1% drops + UVA light (370 nm) → photochemical reaction

27
Q

Lesquels sont FAUX concernant la Descemet’s membrane?
1. Produced by stroma
2. Thickness decreased with age
3. Posterior portion in the « oldest »
4. Descemet’s membrane can be detached after injury and regenerates

A
  1. FAUX : Produced by ENDOTHELIUM
  2. FAUX : Thickness INCREASED with age
  3. FAUX : ANTERIOR portion in the « oldest »
  4. VRAI : Descemet’s membrane can be detached after injury and regenerates
28
Q

Quel est l’épaisseur de Descemet’s membrane? (Naissance versus chez Adulte)

A

Birth : 3-4 um
Adulthood : 10-12 um

29
Q

Quels sont les fonctions de l’endothélium cornéen? (x2)

A

Permiability barrier allowing diffusion of nutrients to the cornea

Pump mechanism to maintain the cornea in a partially dehydrates state

30
Q

Features de l’endothelium cornéen

A

Flat & Hexagonal
Contact with aqueous humor
No reproductive capacity
Visualized with specular microscopy

31
Q

Est-ce que la densité de l’endothélium cornéen increases ou deceases with age?

A

DECREASES
Endothelial density decreases with age.
Significant variation in cell density within various age groups.

32
Q

Quel est la conséquence if cell density decreases to < 500 cells/mm^2 a/n de l’endothélium cornéen?

A

If cell density decreases to < 500 cells/mm^2, CORNEAL EDEMA is likely to appear

33
Q

Comment est maintenu la transparence du stroma?

A

IOP pushes aqueous into stroma.
Ground substance exert an osmotic force that pulls water in stroma.
Transparency maintained BY A PUMP FUNCTION that transports water out of the stroma.

34
Q

Quelle est la constante du stromal water content?

A

Stromal water content is relatively constant at 78%.

35
Q

Lequels sont FAUX concernant les nerfs cornéens.
1. Rich supply of motor nerve
2. 5 large nerve branches enter at the limbus
3. Nerves pass through Bowman’s into the epithelium
4. Loss of myelin sheaths 1-2 mm from the limbus

A
  1. FAUX : Rich supply of SENSORY nerve
  2. FAUX : 12 to 16 large nerve branches enter at the limbus
  3. VRAI : Nerves pass through Bowman’s into the epithelium
  4. VRAI : Loss of myelin sheaths 1-2 mm from the limbus
36
Q

Que deviennent les différentes structures de la cornée en dehors de celle-ci?

A

Corneal epithelium → Conjunctival epithelium

Bowman’s → Lamina propria of conjunctiva & Tenon’s

Corneal stroma → Sclera

Corneal endothelium → Trabecular meshwork

37
Q

Fonctions du Tear Film

A
  1. Moisens & lubricates surface of the globe
  2. Provides a smooth optical surface
  3. Removes desquamated corneal cells and bacteria
  4. Protects the cornea against infection, contains an enzyme lysozyme
  5. Oxygen supply to corneal epithelium
  6. Minimal amount of glucose to corneal epithelium
38
Q

Composition et épaisseur du film lacrymal

A

En ordre :
Lipid layer (Meibomian glands) : 0,1 um
Aqueous layer (Lacrimal glands) : 7,0 um
Mucous layer (Goblet cells) : 0,02 um

39
Q

Quelles structures sécrètent les différentes éléments du tear film (lipid, aqueous and mucous)?

A

Lipid layer (0,1 um) : Meibomian glands
Aqueous layer (7,0 um) : Lacrimal glands
Mucous layer (0,02 um) : Goblet cells

40
Q

Quels sont les fonctions des différentes composantes du tear film?

A

Lipid layer : decreases evaporation
Aqueous layer : prevents epithelial drying
Mucin layer : decreases surface tension and maintains an intact tear film

41
Q

Quels sont les deux autres glandes participant « mineurement » à la sécrétion du lipide dans le Tear Film?

A

Minor secretion :
Sebaceous glands of Zeis
Apocrine glands of Moll

Major secretion : Meibomian glands

42
Q

Où sont situés les glandes de Meibomius?

A

Tarsal plates of upper and lower lids

43
Q

Quelles sont les glandes impliquées dans la sécrétion aqueuse du tear film? (principale et accessoires)

A

Main : lacrymal glands (reflex secretion)
Accessory glands of Krause and Wolfring (basic secretion)

TORIC (17 decks)

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