Ophthalmology 6: Problem Solving - Corneal Ulcers

Question 1

1. Difference between cornea and sclera?
2. Where do the cornea and sclera meet?
   - What structures live here? – what do these structures do?

Answer 1

1. Cornea is made up of organised collagen, sclera made up of disorganised collagen.
2. At the limbus.
   - stem cells of the cornea – create new epithelium and stroma all the time.

Question 2

1. How is the cornea transparent?
2. Corneal structure.

Answer 2

1. Collagen very highly arranged in rows and layers. Also relatively dehydrated to keep it from becoming oedematous and cloudy.
   No vessels, no pigments, non-keratinised.
2. Superficial to deep.
   Epithelium mechanical barrier.
   - lipophilic layer 6-8 cells thick.
   - constantly regrown from basal cells.
   - basal cells replaced by centripetal migration from limbal system cells.
   Endothelium.
   - 1 cell thick, nutrition from aqueous.
   - on Descemet’s basement membrane.
   - contain Na+/K+ATPase physiological pumps to constantly remove water.
   - gets all nutrition from aqueous humour.
   Descemet’s basement membrane = thick specialised basement membrane, which keeps the pressure in the eye.
   Total thickness of canine cornea = 0.55mm.
   Remember the functional lacrimal unit and how thing are interconnected!

Question 3

Exam techniques and diagnostic tests for cornea.

Answer 3

Spot opacities w/ distant direct.
- localise using parallax (gauge depth of opacity).
Examine colour change w/ close direct.
Examine structural change w/ slit beam.
Sampling for cytology/culture?
Fluorescein testing for ulcers.

Question 4

Using a slit beam.

Answer 4

Narrow beam of light.
Highlights contours and deviations in depth.
Also used for spotting particulates in aqueous as ‘flare’ - turbid/muddy.
Check colour and determine if active infection.

Question 5

Sampling.

Answer 5

Sterile cotton bud/Cytobrush over conjunctiva or cornea.
For cytology / C&S / PCR.
Can apply LA first e.g. Proxymetacaine.
NOT after diagnostic drops - affects culture and other dyes.

Question 6

Fluorescein staining.

Answer 6

Available as minims or strips.
Best flushed out w/ saline.
Highlights defects in corneal surface.
Helps check nasal flow of tear drainage w/ ‘Jones’ test.
Fluoresces green when w/ water but orange otherwise.
Mildly irritant - LA first.
Does not adhere to normal corneal epithelium.
Binds to exposed corneal epithelium.
Will penetrate epithelia over time if concentrated so use small amount and flush out w/ saline.

Question 7

Corneal healing process - epithelial repair.

Answer 7

• detachment – basal epithelial cells release attachments to the basement membrane.
• movement – cells slide to fill defect across B.M. (roughly migrate 1mm per day), holding on w/ desmosomes.
• proliferation –epithelial cell mitosis within 24-36hrs. Increase thickness epithelium.
• reattachment – to basement membrane and adhesion complexes.
• normal epithelium in ~2w.
• bacteria in the ulcer will slow the process.

Question 8

Corneal healing process - Stromal repair.

Answer 8

• complex.
• much slower.
• fibroblastic proliferation, new collagen components form.
• new extracellular matrix produced.
• disorganised arrangement of fibres = corneal scarring.
• remodelling occurs over months to years.

Question 9

Corneal healing process - Endothelium repair.

Answer 9

• cells at margin of wound elongate.
• cells get spread thinner and migrate.
• no mitosis possible.
• not as effective.

Question 10

Ocular clinical signs of corneal ulcer.

Answer 10

Epiphora, blepharospasm, conjunctival hyperaemia.
Colour change in cornea.
Pain - behaviour changes, pain face, head shy, pain aggression on approach to examine.
+/- anisocoria:
- asymmetry to pupil size.
- relative miosis on affected side.
- sign of ‘reflex uveitis’.

Question 11

1. Layer of a superficial ulcer.
2. Layer of a deep ulcer.
3. Descemetocoele?
4. Perforation?

Answer 11

1. epithelial ulcer (entire epithelial loss).
2. stromal ulcer (difficult to assess how much stroma lost).
3. complete stromal loss (layer of Descemet’s membrane starts to bulge through ulcer) - potential for rupture.
4. rupture of entire cornea, including Descemet’s membrane.

Question 12

Approach to a suspected corneal ulcer.

Answer 12

Thorough ophthalmic exam.
Assess depth of ulcer.
Check fluorescein uptake.
Aim to identify and treat inciting cause e.g.:
- abnormal lids.
- exposure e.g. ineffective blink.
- aberrant hairs.
- foreign body.
- KCS.
- any other change to Surface Lacrimal Unit.

Question 13

Removal of foreign body from the eye.

Answer 13

E.g. grass seeds or plant matter.
Wedged into 3EL or conjunctiva, deep in fornix.
Sedate for thorough exam.
Grasp and remove FB, flush eye w/ saline jet through needle.

Question 14

Approach once FB removed.

Answer 14

Should heal rapidly w/ supportive care (w/in 1w):
- analgesia (systemic NSAIDs).
- ABX prophylactically.
- lubrication.
- +/- buster collar.
Minimal scar formation.
E.g. incidental scratch / FB removed.

Question 15

Reflex uveitis.

Answer 15

2’ to anterior ocular pain e.g. ulcer.
Occasional finding.
Reflex causes spasm of ciliary body.
Miosis.
Painful spasm like ‘cramp’.
Other signs of uveitis may develop.
Treat w/ mydriatics e.g. atropine.
Can give NSAIDs systemically.

Question 16

Blue - oedema.

Answer 16

May see blue tinge in area of anterior eye before applying fluorescein.
Epithelial defect leads to focal oedema:
- diffuse.
- focal.
- hazy.

Question 17

White colour change in healed ulcers.

Answer 17

Corneal fibrosis - scarring.
Inflammatory cell infiltrates initially.
Remodel stroma and return to near normal structure.
Scars contract but remain visible.
Scars do not uptake fluorescein.
Once healed, can stop ABX and stop analgesia once comfortable.

Question 18

Inherited corneal dystrophy.

Answer 18

Non-pathological white changes.
Bilateral.
Recognised in young dogs e.g. CKCS, husky, Dachshund.
Lipid/mineral dystrophy.
Little progression or impact on vision.
Rarely ulcerate.
No treatment in most cases.

Question 19

Lipid deposits / mineral deposits.

Answer 19

Both are uncommon.
Seen in older dogs, likely to be systemically ill.
Can sometimes ulcerate quite dramatically.
Lipid deposits may form an arc and are associated w/ hyperlipidaemia or endocrinopathies so recommend bloods.
Mineral deposits are associated w/ endocrine disease and occur in geriatric patients.
White corneal colour changes w/ no ulceration might need some further investigation.

Question 20

SCCED.

Answer 20

Spontaneous chronic corneal epithelial defect.
Superficial ulcer not heal in 1-2w.
Middle aged dog (average 7-9yrs).
ANY BREED - commonly SBT/boxer.
Can persist for weeks, months, even years if not treated effectively.
No apparent inciting cause.
NOT ‘wrong’ ABX.
Also called ‘Boxer ulcers’, ‘indolent (lazy) ulcers’.

Question 21

SCCED pathogenesis.

Answer 21

Not fully understood.
Poor epithelial adhesion to stroma.
Abnormal basement membrane.
Abnormal superficial stroma - has a superficially hyalinised acellular zone.
Typically a glancing abrasion knocks off poorly adhered epithelium.
Often created a ‘flap’ of loose epithelium.

Question 22

SCCED clinical signs.

Answer 22

Superficial ulcer (epithelium loss only).
Loose epithelial edges.
Halo of fluorescein.
‘Under-run’ edges.
Minimal corneal oedema (easy to miss).
Potential neovascularisation in time.
Variable pain.
Can recur in novel corneal sites.

Question 23

SCCED supportive medical treatment.

Answer 23

Prophylactic topical ABX.
- e.g. fucidic acid BID (L), or chloramphenicol TID-QID (off-L).
Lubrication.
Systemic NSAID analgesia (meloxiam, paracetamol).
+/- topical atropine if reflex uveitis/miosis.
+/- oral doxycycline 5mg/kg SID may promote epithelialisation.
Buster collar.
BUT unlikely to heal w/ meds alone as defective epithelium persists.

Question 24

SCCED surgical treatment.

Answer 24

Epithelial debridement.
Remove loose, detached epithelium.
Use dry, sterile cotton buds.
Disrupts anterior stroma / removes hyalinised zone.
Alone overall 50% healing rate.
Can be repeated after 7-14 days.
Under LA (Proxymetacaine).
SCCEDs are the only ulcer you should debride!

Question 25

SCCED second line treatment if cotton bud debriding does not work.

Answer 25

Punctate keratotomy = anterior stromal puncture - making holes in the eye w/ hypodermic needle.
or
Grid keratotomy - scratching train tracks across surface of the ulcer.
or
Diamond burr debridement - Spinning burr gently moved over affected site to remove superficial abnormal cornea w/ 85% success rate.

Both techniques require LA +/- sedation.
Both use 25G or insulin needle.
Both can be repeated after 7-14 days.
Both have 80% success rate.

Question 26

What can be done post SCCED surgery?

Answer 26

Additional support w/ bandage contact lens.
- physical protection.
- improves comfort.
- holds tear over ulcer bed.
- depot of medication.
- seems to shield migrating epithelial cells.
- Potential complication of bacterial keratitis (uncommon) – be weary about use if infection already suspected.
- improves success rate.

Question 27

Deep ulcers.

Answer 27

Need to look at it from different angles.
Slit beam.
Mid to deep stromal loss.
Looks like a crater.
Trauma/FB or could be melting.
Further tests employed urgently.
- swab for C&S (48hrs+).
- swab for cytology (15mins).
Fragile eye do care not to increase IOP.
Requires surgical structural support and always committed medical management.

Question 28

Melting ulcers.

Answer 28

Collagenolysis / keratomalacia.
Matrix Metalloproteinases and proteases liquify stroma.
Soft and flocculant stroma, slight wobbles w/ globe motion.
Commonly have 2’ bacterial infection.
- pseudomonas.
- B-haemolytic Strep.
- Mya be sterile.
Common in brachycephalic patients, in central corneal location.
Increased comfort could be a bad sign as nerve endings digested.
Can progress to ruptured globe w/in 24hrs w/o tx.
Guarded Px.

Question 29

Melting ulcers - medical support.

Answer 29

Intensive - every 1-2hrs.
Topical ABX - empirical until cytology or C&S.
– Fluoroquinolone Ofloxacin justified for use.
Systemic broad spectrum antibiotic Doxycycline.
Antiprotoelytic drops - serum, plasma, EDTA, N-Acetylcysteine.
Lubrication.
Analgesia.
Systemic NSAIDs +/- atropine for uveitis.
Buster collar.
Lid hygiene.
Can be effective to clinical resolution.

Question 30

Deep/melting ulcers surgical management.

Answer 30

Referral level.
3EL flap / tarsography / Gunderson flap.
Reconstructive corneal surgery.
- cover defect.
- facilitate corneal healing.
- conjunctival grafts.
- corneo-conjunctival transposition.
- corneal implants or transplants.
Consider as welfare issue if sub-optimal treatment.
A fair option to enucleate.

Question 32

Read the cornea…
1. Ulcer on edge?
2. Ulcer in centre?
3. Recurrence of ulceration?

Answer 32

1. Look for focal mechanical issue.
2. Consider exposure.
3. Consider KCS or repeated insults.

Question 33

Fluorescein staining patterns.

Answer 33

‘Simple’ epithelial ulcer.
- stain adheres to exposed stroma.
- defined edges.
- curve preserved.
SCCED.
- stain underruns detached epithelium.
- hazy ulcer edge.
- corneal curve preserved.
- ‘halo’ effect.
Stromal ulcer:
- stain adheres to exposed stroma.
- defined edges.
- ‘crater’ effect.
Deepest ulcer (Descemetocoele):
- stain adheres to exposed stroma.
- unstained Descemet’s membrane.
– ‘bullseye’ effect.
Melting ulcer:
- stain adheres to exposed stroma.
- fluorescein diffuses into unhealthy stroma.
- messy edges.
- loss of contour.

Question 34

What can neovascularisation tell you about the depth of an ulcer?

Answer 34

Superficial or early stromal ulcer:
- vessels grow towards ulcer.
- point to the problem.
- branching trees of bright red vessels.
- extend from bulbar conjunctiva.
- seen to cross limbus,
- take immunity to site for healing.
Deep stromal ulcer / perforation:
- likely concurrent uveitis.
- fine, short, straight vessels.
- from within limbus.
- not seen to cross limbus.
- “eye is shouting for help”.
- vessel length = duration of injury.