Hypoxia and corneal responses

Question 1

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

Answer 1

Microcysts
Vacuoles
Epithelial Plug

Question 2

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

Answer 2

Oedema
Neovascularisation
Microbial and sterile keratitis

Question 3

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

Answer 3

Bedewing
Blebs
Polymegathism

Question 4

How do microcysts appear on observation?

Answer 4

small, spherical inclusions with light reversed inside them

Question 5

How long does it take microcysts to appear?

Answer 5

1 week to 2 months after starting CL wear

Question 6

What is within microcysts?

Answer 6

Cellular debris from cells killed by hypoxia

Question 7

How do microcysts develop?

Answer 7

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

Question 8

Where will the most microcysts be found?

Answer 8

Where the thickest part of the lens is

Question 9

What is microcyst rebound?

Answer 9

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

Question 10

How do vacuoles appear on observation?

Answer 10

small, spherical inclusions, light not reversed

Question 11

What is within vacuoles?

Answer 11

Gas and fluid

Question 12

Where will the most vacuoles be found?

Answer 12

Mid-peripheral cornea in groups of 2-4

Question 13

Why does corneal oedema form due to hypoxia?

Answer 13

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.

Question 14

What are striae in corneal oedema?

Answer 14

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

Question 15

What are folds in corneal oedema?

Answer 15

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

Question 16

What is haze in corneal oedema?

Answer 16

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

Question 17

At what point does corneal oedema start to affect VA?

Answer 17

Once it’s over 20% oedema

Question 18

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

Answer 18

Over 15% oedema

Question 19

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

Answer 19

4 hours-7 days

Question 20

What causes corneal neovascularisation?

Answer 20

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

Question 21

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

Answer 21

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

Question 22

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

Answer 22

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

Question 23

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

Answer 23

Minimise toxic/allergic response - change sols
Monitor

Question 24

How does bedewing appear on observation?

Answer 24

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

Question 25

Why does bedewing occur?

Answer 25

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

Question 26

What are the sxs of bedewing?

Answer 26

Partial/total CL intolerance Stinging Red eyes Corneal clouding

Question 27

How long does it take for bedewing to resolve?

Answer 27

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

Question 28

How do blebs appear on observation?

Answer 28

Black, non-reflecting areas of the corneal endothelium

Question 29

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

Answer 29

100% Within 10 mins of insertion

Question 30

What causes blebs?

Answer 30

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

Question 31

What are guttata? What could they be mistaken for?

Answer 31

Permanent, progressive accumulation of collagen on DM Mistaken for blebs

Question 32

What can guttata be a precursor to?

Answer 32

Fuch's endothelial dystrophy

Question 33

How do guttata appear on obervation?

Answer 33

Dark spot in central cornea, larger than blebs

Question 34

What is Fuch's endothelial dystrophy?

Answer 34

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

Question 35

What is polymegathism?

Answer 35

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

Question 36

Why does polymegathism occur?

Answer 36

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