Ophthalmology: Cornea

Question 1

Describe the anatomy of canine conjunctiva?

Answer 1

• Thin mucous membrnae
• Lines the lids reflected at the dorsal and ventral fornices onto the globe
• Covers nicitating membrane
• Contains globles cells- mucus fraction of tear

Question 2

1. What is the normal colour of mucus from the conjunctiva?
2. What colour does it change to with conjunctivitis?

Answer 2

1. Off-white, darkens to grey with air
2. Yellow/green

Question 3

1. What are primary causes of non-specific conjunctivitis?
2. How is it usually treated?

Answer 3

1. Wind, dust, trauma- oppertrunistic
2. Fusidic acid- effective against staphs or broad spec AB (gentamycin)

If persist look for another factor

Question 4

What produces the tear film in the dog?

Answer 4

Three layers
* Mucus- globlet cells of the conjunctiva
* Aqueous- lacrimal gland/nicitating membrane
* Lipid- tarsal glands

Question 5

1. What is KCS or Dry eye?
2. What are the clinical signs?

Answer 5

1. Keratoconjunctivitis sicca- deficiency of aqueous tear film production
2. Clinical signs
   * Loss of corneal reflex
   * Corneal ulceration- acute
   * Superficial keratisis
   * Corneal pigmentation
   * Diffuse conjunctivitis
   * Mucopurulent occular discharge

Most are chronic and progressive

Question 6

What breeds are represented for KCS?

What can cause it?

Answer 6

• WHWT
• Cocker
• Brachycephalics
• Bulldogs

Upper lid trichiasis, congenital, neurogenic

Question 7

How is KCS diagnosed?
How is it medically managed?

Answer 7

Diagnosis
* Schirmer tear test strips
* Measure flow over 1min
* 15mm minimum

Medical managment
* Tear stimulants- cyclosporin or tarcolimus
* Lubricants

Question 8

1. What is dry eye-dry node syndrome?
2. How is it treated?

Answer 8

1. One eye and ipsilateral nasal planum suffer loss of gland function- neurogenic
2. Pilocarpine eye drops in food

Question 9

How do tears drain?

Answer 9

Naso-lacrimal duct- near the medial canthus

Question 10

How are tear drainage problems investigated and diagnosed in dogs?

Answer 10

• Rule out painful causes of lacrimation
• Examine medial canthus for entropion
• Establish normal nasolacrimal puncta
• Instil 1 drop of fluorescein into both eyes
• Flush with saline and wait
• 3-4 mins should flow into nares
• Flush system- sedate, lacrimal cannula

Brachys negative- weird

Question 11

What are common causes and treatments of tear drainage problems?

Answer 11

Congenital micropuncta
* Golden retriever, cocker spaniel
* Thin membrane- excised

Dacryocysitis- infection/inflammation of duct from FB

Epiphora- permanent opstruction- bypass surgery

Question 12

What are the 4 layers of the cornea?

What innervates the cornea?

Answer 12

1. Outer epithelium- needs tears
2. Stroma- consisting of fine collagen fibrils arranged in lamellae- precise arrangment
3. Descemets membrane- acellular basemend membrane
4. Endothelium- monolayer of flat cells

Opthalmic branch of trigeminal

Question 13

What is required for the normal cornea to be transparent?

Answer 13

• No keratin
• No pigment
• Avascular
• Precise arrangment of collagen in stoma- no oedema, scar tissue, inflammatory tissue

Question 14

What is a corneal ulcer?

Answer 14

A full thickness defect in the epithelium of the cornea- outermost layer

Very painful- potential for deeper progression

Question 15

How is corneal ulcer diagnosed?

Answer 15

• Corneal contour is disrupted often with surrounding oedema
• Fluorescein- washes of intact, stains exposed

Question 16

What could a ‘clear non-staining area in the centre of a ring’ mean with a fluorescein stain

Answer 16

• The descemets membrane does not stain
• Therefore could indicate a serious deep ulcer
• Check for perforation- space between iris and cornea

Question 17

What can be a primary cause of corneal ulcers?

Answer 17

Factors causing mechanical damage
* Trauma, entropion, FB etc

Factors contributing to unhealthy superficial corneal environments
* KCS
* neurogenic

Inherent corneal defects
* Indolent ulcers
* Chronic oedems

Pugs are just high risk for ulcers, both getting and deterioration

Question 18

What should non-specific medical support consist of?

Answer 18

• Broad spec, topical ABs
• Lubricant?
• Atropine- relieves pupil spasm
• Serum or other anti-collagenases

Question 19

Why are topical steroids contraindicated for corneal ulcers?

Why are local anaesthetic drips contraindicated for corneal ulcers?

Answer 19

Steroids
* Inhibit epithelial healing
* Predispose to infection
* Potentiate the action of collagenases, causing melting

LA
* Only lasts 1hr
* toxic to epithelium
* Prevents blinking

Question 20

Why is surgical treatment of ulcers controversial?

Answer 20

Now controversial: third eyelid flap
* Obscures the eye
* Interferes with medication
* Not adequate for deep ulcers or indolent

Surgery is required for deep ulcers with no vascular ingrowth

Question 21

1. What breeds more commonly ave indolent ulcers?
2. How does it appear?
3. How is it treated?

Answer 21

1. Boxer, staffie, corgi
2. Very shallow ulcer with only the epithelium lost and underruning of the epithelium
3. Medical/third eyelid flap ineffective- must be debrided
   LA, cotton wool around the tip of an artery forceps- scalpel blade in scraping action

Question 22

What are the non-ulcerative corneal conditions?

Answer 22

• Pigmentary keratitis
• Senile corneal endothelial dystrophy
• Lipid depositions
• Dermoid
• Pannus
• Lacerations/penetrations

Question 23

What casues pigmentary keratitis?

Answer 23

Pigment is carried from the limbus along with new blood vessels in reponse to superficial damage
* Not primary
* Does not regress

Question 24

What causes senile corneal enothelial dystrophy?

Answer 24

Progressive degeneration of the endothelium leads to chronic corneal oedema

Can rupture leaving ulcers

Question 25

Where are the two most common lipid depositions of the cornea?

Answer 25

Paracentral lipid dystrophy * Sub-epithelially in the anterior third of the cornea * No pain, vascularisation, no systemic problem * Tx- superficial keratectomy- not necessary Lipid keratopathy * Deposition of lipids in association with inflammation and vascularisation * Usually secondary to previous injury or ulceration

Question 26

What is corneal dermoid?

Answer 26

* A patch of well differentiated skin present congenitally on the cornea usually at the lateral limbus Tx- superficial keratectomy

Question 27

What is pannus?

Answer 27

* A chronic superficial vascular keratitis- GSD * A front of pigment, inflammatory tissue and vessels advances across the cornea * Infiltration is sub-epithelial and therefore fluorescein negative Tx- topical steroids or cyclosporin