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CLO > Cornea > Flashcards

Cornea Flashcards

1
Q

6 Layers of the cornea

A

Epithelium

Anterior limiting lamina

Stroma

Dua’s layer

Posterior limiting lamina

Endothelium

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2
Q

Thickness: Epithelium

A

55um

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3
Q

Thickness: Anterior limiting lamina

A

8-10um

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4
Q

Thickness: Stroma

A

500um

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5
Q

Thickness: Dua’s layer

A

15um

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6
Q

Thickness: Posterior limiting lamina

A

8-10um

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7
Q

Thickness: Endothelium

A

5um

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8
Q

Corneal: Width

A

11.6mm

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9
Q

Corneal: Anterior height

A

10.6mm

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10
Q

Corneal: Centre thickness

A

540um

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11
Q

Corneal: Edge thickness

A

0.7mm

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12
Q

Corneal: Anterior radius

A

7.8mm

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13
Q

Corneal: Posterior radius

A

6.7mm

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14
Q

Corneal: Refractive index

A

1.376

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15
Q

Corneal: Refractive power

A

~42D

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16
Q

Corneal Overview

A

Transparent outer coat

Several layers of connective tissue

Avascular and specialised structure = transparency

Mechanical protection and sensory innervation = blink reflex

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17
Q

What can reduce corneal sensitivity

A

Systemic diseases like diabetes

18
Q

What can innervation damage cause

A

Anaesthesia - loss of reflex lacrimation and lid closure

19
Q

Corneal innervation

A

Nerve fibres on cornea unmyelinated for transparency

Schwann cells myelinate nerves towards peripheral cornea

Leaves as bundles to join ciliary nerve from ophthalmic branch of trigeminal nerve

20
Q

Cell types making up epithelium

A

Squamous cell - 2 layers

Wing cell - 2 to 3 layers

Columnar cell - 1 layer

21
Q

Features: Epithelium

A

Stratified

Non keratinised

5-6 layers

Made up of 3 different cells

22
Q

What structures are involved in corneal healing

A

Epithelium

Stroma

Nerves

Lacrimal glands

Tear film

23
Q

Name the 4 phases of corneal healing

A

Latent phase

Migration

Proliferation

Attachment

24
Q

Healing times for superficial damage and full thickness defect

A

24hrs for superficial

7 days for full defect

25
Q

At what point does scarring occur

A

Damage deeper than anterior limiting lamina will heal but scar

26
Q

Latent phase (5)

A

Lacrimal glands change tear makeup/quantity

Growth factors released from tears

Damaged cells go through cell death process

Fibres aid adhesion or migrating cells

Desmosome attachments weaken

27
Q

Migration

A

Surrounding cells flatten and slide together along wound bed

Miosis does not occur yet

28
Q

Proliferation

A

Cells proliferate upwards

Cell division accelerated - new cells move upward

Zonular occlusions form 1st, epithelial 2nd and then glycolax

29
Q

Attachment

A

Restoration and attachment of desmosomes and heridesmosomes

Wound closure 2-4 days - full attachment full week

30
Q

Function: Epithelium

A

Smooth hydrophilic refracting surface

Metabolic exchange and pathogen/bacteria protection

Rapid regeneration/mechanical protection - blink reflex

31
Q

Function: Anterior limiting lamina

A

Anchor site for epithelium

Tough layer for mechanical support

32
Q

Features: Anterior Limiting Lamina

A

8-10um thick

Acellular zone with collagen fibres

Posteriorly woven with anterior stroma

Sensoru nerve fibres to innervate epithelium

Layer separates epithelial growth factors to avoid scarring

33
Q

Function: Stroma

A

Mechanical strength and stability

Maintains homogeneity for transparency

Regularity of fibre arrangements produce diffraction grating

34
Q

Features: Stroma

A

Formed with layers of collagen and fibroblasts between

Collagen fibrils evenly spaced in parallel bands

Layers include keratin sulphates to aid corneal hydration

35
Q

Location of Dua’s Layers

A

Between stroma and posterior limiting lamina

36
Q

Features: Dua’s Layer

A

Layers of collagen laying in longitudinal, transverse and oblique direction

Made up of 5-8 layers

Very strong ~700mmHg before rupture

Important for glaucoma treatment response and keratoplasty surgery techniques

37
Q

Function: Posterior limiting lamina

A

Structural base for endothelium

38
Q

Features: Endothelium

A

Single layer

Metabolically active = many mitochondrias

Cannot regenerate

Cell membrane creates barrier to prevent free flow

Vesicles within regulate corneal hydration and aid transport of metabolites from aqueous

39
Q

Corneal Transparency: Nerves and vessels

A

Avascular - episcleral loops enter the cornea up to 1mm at limbus

Unmyelinated nerves until 0.5mm from the limbus

Homogenous refractive index - maintained by consistent water content

40
Q

Corneal Transparency: Features

A

Regularity of fibrils

Parallel spacing = diffraction grating

Spaced less than then wavelength of light

Light incident normally travels undeviated

Light incident at an angle away from the 4mm centre will have reduced transmission

UVB/UVC mostly absorbed as their wavelength less than fibril spacing

CLO (13 decks)

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