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Contact Lenses > Hypoxia and corneal responses > Flashcards

Hypoxia and corneal responses Flashcards

1
Q

What pathology can occur in the corneal epithelium due to hypoxia?

A

Microcysts
Vacuoles
Epithelial Plug

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2
Q

What pathology can occur in the corneal stroma due to hypoxia?

A

Oedema
Neovascularisation
Microbial and sterile keratitis

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3
Q

What pathology can occur in the corneal endothelium due to hypoxia?

A

Bedewing
Blebs
Polymegathism

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4
Q

How do microcysts appear on observation?

A

small, spherical inclusions with light reversed inside them

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5
Q

How long does it take microcysts to appear?

A

1 week to 2 months after starting CL wear

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6
Q

What is within microcysts?

A

Cellular debris from cells killed by hypoxia

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7
Q

How do microcysts develop?

A

Form in deepest epithelial layers due to disorganised cell growth and move forward. Stain once on ocular surface

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8
Q

Where will the most microcysts be found?

A

Where the thickest part of the lens is

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9
Q

What is microcyst rebound?

A

Number increase initially once CLs not worn due to increased metabolism and growth of epithelium from increased oxygen levels

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10
Q

How do vacuoles appear on observation?

A

small, spherical inclusions, light not reversed

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11
Q

What is within vacuoles?

A

Gas and fluid

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12
Q

Where will the most vacuoles be found?

A

Mid-peripheral cornea in groups of 2-4

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13
Q

Why does corneal oedema form due to hypoxia?

A

Hypoxia induces anaerobic respiration - this has a by product of lactate/lactic acid which accumulates.
More water enters the cornea too and the endothelial pump is unable to balance the excess fluid.

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14
Q

What are striae in corneal oedema?

A

White, fine, vertical lines in posterior stroma caused by fluid separation of posterior fibrils

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15
Q

What are folds in corneal oedema?

A

physical buckling of the posterior stroma
seen as depressed grooves or raised ridges in endothelium

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16
Q

What is haze in corneal oedema?

A

Hazy, granular appearance to stroma due to gross separation of fibrils

17
Q

At what point does corneal oedema start to affect VA?

A

Once it’s over 20% oedema

18
Q

At what point does corneal oedema start to make the cornea lose transparency?

A

Over 15% oedema

19
Q

How long does it take corneal oedema to resolve with no CL wear?

A

4 hours-7 days

20
Q

What causes corneal neovascularisation?

A

Combination of hypoxia, angiogenic suppression, vasostimulation and neural control factors

21
Q

How should neovascularisation be managed if it’s over grade 1?

A

Refit to RGP or SiH
Reduce WT
Stop EW
Decrease mechanical stimulation

22
Q

How should neovascularisation be managed if it’s over grade 2?

A

STOP LENS WEAR
Px must be managed carefully if wants to return to lens wear

23
Q

How should neovascularisation be managed if it’s under grade 1?

A

Minimise toxic/allergic response - change sols
Monitor

24
Q

How does bedewing appear on observation?

A

small white inclusions on inferior central cornea (endothelium) which become pigmented, reversed illumination

25
Q

Why does bedewing occur?

A

Due to inflammation - cells from iris and ciliary body engulfed into endothelium

26
Q

What are the sxs of bedewing?

A

Partial/total CL intolerance
Stinging
Red eyes
Corneal clouding

27
Q

How long does it take for bedewing to resolve?

A

Sxs: 3-5 days
Bedewing: 3-5 months

28
Q

How do blebs appear on observation?

A

Black, non-reflecting areas of the corneal endothelium

29
Q

What percentage of CL wearers will get blebs and how quickly do they appear?

A

100%
Within 10 mins of insertion

30
Q

What causes blebs?

A

Reversible localised oedema (due to increased lactic acid and carbonic acid) causes cells to bulge posteriorly

31
Q

What are guttata? What could they be mistaken for?

A

Permanent, progressive accumulation of collagen on DM
Mistaken for blebs

32
Q

What can guttata be a precursor to?

A

Fuch’s endothelial dystrophy

33
Q

How do guttata appear on obervation?

A

Dark spot in central cornea, larger than blebs

34
Q

What is Fuch’s endothelial dystrophy?

A

An autosomal dominant inherited condition which causes reduced VA due to corneal oedema and pain due to exposed corneal nerve endings.

35
Q

What is polymegathism?

A

Endothelial cell density and regularity irreversibly reduces, due to cell death, leaving remaining cells to fill gaps. No new cells created.

36
Q

Why does polymegathism occur?

A

Natural aging process but accelerated by CL wear due to acidic shift
Due to loss of endothelial pump function

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