Opthalmology

Question 1

List the signs of the painful eye.

Answer 1

Epiphora, ptosis, miosis, photophobia, blepharospasm, enophthalmos, discharge, swelling, entropion (is a condition in its own right)

Question 2

Discuss the process of an ocular exam in horses.

Answer 2

1. Hx including duration of Cx, mediations tried, previous episodes of a similar thing?
2. Distance exam + testing ocular reflexes including PLR + menace (every time)
3. Sedate - xylazine 0.3-0.5mg/kg IV or detomidine 0.01-0.02mg/kg IV +/- butorphanol 0.01mg/kg IV
4. Local nerve blocks if you are concerned about globe rupture or the horse is particularly resistant to examination
5. External to internal examination with focal light sources - adnexa, cornea, iris, chambers, lens, retina
6. Pupillary dilation for examination of retina
7. Examination under the third eyelid - use topical anaesthesia (proparacaine HCl 0.5%, proxymetacaine HCl 0.5%)
8. Fluorescein stain!!!

Question 3

Which dilating agent is used for pupillary dilation in the ocular exam of a horse?

Answer 3

Tropicamide HCl 1%

Question 4

Describe the importance of the ocular exam in the pre-purchase examination.

Answer 4

It is a legal procedure which documents any abnormal findings + provides a risk assessment of current and future vision of the horse.
Important for safety, suitability for intended purpose and insurance.

Question 5

What structures are included in the uveal tract (middle/vascular tunic)?

Answer 5

Iris, corpora nigra, ciliary body, choroid, tapetum lucidum, lens, zonular fibres, anterior + posterior chamber

Question 6

You are doing an ocular exam and need to do local nerve blocks. You decide to do a supraorbital nerve block. Which cranial nerve is this branch from? What is that doing to desensitise and achieve?

Answer 6

Cranial nerve VII
Desensitise the medial 2/3 of the upper eyelid
Stops pain - blocks sensory function

Question 7

You are doing an ocular exam and need to do local nerve blocks. You decide to do a auriculopalpabral nerve block. Which cranial nerve is this branch from? What is that doing to desensitise and achieve?

Answer 7

Cranial nerve V
Desensitises motor innervation of the upper eyelid
Stops blinking

Question 8

A horse is presenting in summer with epiphora + ocular discharge at the medial canthus. The conjunctiva are hyperaemic + oedematous. What is your main differential and what treatment may be required for this horse?

Answer 8

DDx - conjunctivitis with obstruction of the nasolacrimal duct by mucous/pus
Tx - nasolacrimal duct flush with sterile water for injection or NaCl, systemic antiinflammatories (PBZ) +/- antibiotic ointment

Question 9

Which signalments of horse are more prone to entropion?

Answer 9

Premature or dysmature foals - have decreased periorbital fat
Dehydrated foals
Foals with ocular pain leading to turning in of the eyelid

Question 10

You are called out to see a week old foal to do general health checks. You decide to test some ocular reflexes and cannot get a positive menace response. What are your thoughts and next steps?

Answer 10

Nothing
Foals dont have a menace response in the first few weeks of life

Question 11

Discuss the treatment of entropion.

Answer 11

Address primary disease process - i.e. dehydration
Temporary correction with vertical mattress sutures (outward roll the eyelid and suture it in place)

Question 12

You are called out to see a horse that has gone through a particularly tall fence and has a traumatic laceration to the right eye with a flap on the lower eyelid not involving the corneal margin (thankfully). What should you do with the flap? What are the appropriate next steps?

Answer 12

Leave the flap attached and suture it - it has excellent blood supply, good healing tendency

Do a full globe assessment of the rest of the eye
Sedate, administer local anaesthesia and close the laceration in 2 layers (subcut and skin)
Give a tetanus booster
Consider referral for show horses

Question 13

An owner calls you about a growth on their horses eyelid. What are your main differentials and how will you differentiate them?

Answer 13

Equine periocular sarcoid
Squamous cell carinoma
Cutaneous habronemiasis
Granulation tissue
Melanoma
Papilloma

Sample with a swab, cytology brush or scalpel scraping and send for cytology + histopathology

Question 14

Describe the clinical signs you might expect to see in a horse with a corneal ulcer.

Question 15

How do we diagnose a corneal ulcer?

Question 16

Design an appropriate treatment plan for an uncomplicated corneal ulcer - superficial, small and sustained <2d ago.

Answer 16

Management in the field with no further diagnostics
Prophylactic antibiotics with chloramphenicol (Clorsig) or combination bacitracin-polymixin B and neomycin (Tricin) - 1cm strip ointment/2-3 drops to affected eye BID-TID
2.2mg/kg phenylbutazone PO SID-BID 5d course +/- an initial dose of 1.1mg/kg IV flunixin at time of assessment
+/- mydriatics - atropine as required but often only once or EOD for simple cases
REVISIT IN 2-3 DAYS - restain them, have owner treat ulcer until negative for stain, if it comes complicated then re-evaluate and adjust treatment plan

Question 17

You are presented with a horse that has increased corneal opacity. What major categories are you thinking could be contributing?

Answer 17

Oedema
Scar tissue or fibrosis
Cellular infiltration
Neovascularisation
Pigments or precipitates

Question 18

Differentiate the 3 subtypes of complicated corneal ulcers from superficial or uncomplicated ulcers.

Answer 18

Uncomplicated ulcers are generally epithelial injury with minimal anterior stromal loss

Complicated non-healing - >7d not healed
Penetrating - stroma involved to varying depth up to Descemet’s membrane
Perforating - cornea penetrated and anterior chamber entered + directly involved (might have fibrin plugging the hole or iris prolapsing)

Question 19

What are the causes of non-healing ulcers?

Answer 19

Failure to epithelialise
Infection - fungal, bacterial
Ongoing exposure as n distichiasis, FB, scratching
Failure to induce a significant inflammatory resopnse - generally older horses and PPID
Poor owner and horse compliance

Question 20

Name the most common fungal agents involved in complicated fungal ulcers/keratomycosis.

Answer 20

Aspergillus and Fusarium

Question 21

Name the most common bacterial species involved in melting ulcers/keratomalacia.

Answer 21

Beta haemolytic Streptococcus and Pseudomonas aeruginosa

Question 22

For which types of corneal ulcer would you refer for management in a hospital or for emergency treatment if you were working in the field?

Answer 22

Perforating ulcers - if focal, acute puncture, otherwise most just need enucleation which can be done in the field if confident
Deep penetrating ulcers
Descemetocele
Keratomalacia/melting ulcer
Fungal infection/keratomycosis
Large superficial ulcers
Non healing ulcers after attempting in field management
Poor treatment compliance due to horse behaviour or owner ability
If the owner wants a referral then refer it

Question 23

Describe the in-hospital management of complicated corneal ulcers.

Answer 23

IV catheter for fluids
Subpalpebral lavage system (SPL) - allows us to give frequent antibiotics +/- antifungals q1-2h, atropine q4-6h, + anti-collagenases including EDTA and autologous serum to prevent epithelium from melting
Close monitoring

Surgical debridement for melting ulcers + stromal abscesses
Conjunctival gradting
Temporary tarsorrhaphy
Enucleation - can also be done in the field

Question 24

Describe the clinical signs expected for uveal tract conditions.

Answer 24

Miosis
Blepharospasm
Attempts to scratch at the eye
Conjunctival hyperaemia
Episcleral injection
Epiphora
Abnormal contents in anterior chamber - aqueous flare, fibrin clots, hypopyon, hyphema

Question 25

What is reflex uveitis?

Answer 25

A generally transient and mild reflex axonal uveitis associated with corneal disease

Question 26

List 3 causes of acute active uveitis.

Answer 26

Trauma
Bacteria - Lepto, Brucella, Rhodococcus equi
Viral - EIV, EHV1 and 2
Parasitic - Toxoplasma
Neoplasia
Any other cause of blood/ocular barrier breakdown

Question 27

Describe the advanced stage of chronic/end-stage uveitis.

Answer 27

Shrunken eye = Phthisis bulbi
Cataract formation
Retinal detatchment
Synechiae

Question 28

Which breed is predisposed to equine recurrent uveitis?

Answer 28

Appaloosa

Question 29

Describe how to diagnose equine recurrent uveitis.

Answer 29

Hx of several recurrent or persistant episodes of uveitis
Presence of characteristic Cx - often bilateral
Decreased IOP
Direct exam - punctate chorioretinitis (bullet holes)
Loss of vision

Question 30

Explain management and treatment of equine recurrent uveitis.

Answer 30

Aggressive initial therapy
Flyveil (light protection), reduce fly exposure + possible environmental triggers
Topical atropine 1% SID to BID or as required to reduce discomfort
Systemic corticosteroids (dexamethasone) + NSAIDs (flunixin, PBZ)
Topical prednisolone (contraindicated if corneal ulceration so STAIN THE EYE) or diclofenac - use topical anti-inflammatoeis with caution
+/- intravitreal gentamicin if +ve for Lepto
+/- subconjunctival triamcinalone
+/- topical cyclosproine A (immunosuppressant)
+/- suprachoroid cyclosporine A implant
+/- vitrectomy or pars plana vitrectomy