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Equine Studies > Common ocular conditions of the Equine eye > Flashcards

Common ocular conditions of the Equine eye Flashcards

1
Q

What are the layers of the cornea?

A
  1. Epithelium
  2. Stroma
  3. Descemet membrane
  4. Endothelium
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2
Q

What is the difference in Fluorescein staining between a superficial and deep ulcer?

A

Superficial; sharp edges, no epithelial under-run, no stain migration
Deep; epithelial under-run +/- stain migration

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3
Q

What is the difference between a superficial and deep corneal ulcer?

A

The stroma is intact (only epithelium broken) in a superficial ulcer

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4
Q

What is the cause and treatment of Keratomalacia “melting ulcer”

A

Cause:
Activation and/or production of proteolytic enzymes (by corneal epithelial cells, leucocytes and pseudomonas)
Treatment:
Early aggressive therapy!
Topical EDTA (anti-enzymatic)
Topical Tetracycline or Doxycycline (immunomodulatory)
NSAIDs (flunixin)

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5
Q

What is the treatment for Descemetocele?

A

Same as keratomalacia or surgical (conjunctival flap)

High risk of rupture

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6
Q

What are the characteristics of Descemetocele?

A

Fluorescein negative

Not necessarily very painful (sparse nerve endings)

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7
Q

What is the treatment for full thickness corneal laceration?

A

Clean iris, push back in, stitch with tiny sutures, re-inflate eye

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8
Q

What are the characteristics and treatment for a stromal abscess?

A

Fluorescein negative
Very reactive and +++ inflammation
Lipophilic antimicrobials: Chloramphenicol
Surgery to expose the abscess, debridement, corneal grafting

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9
Q

What are the characteristics and treatment for Viral keratitis (EHV-2)

A

Multiple, superficial, white, punctate or linear (dendritic) opacities
High degree of ocular pain (relative to damage)
Topical Aciclovir/Ganciclovir

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10
Q

What is the characteristics and treatment for Fungal keratitis?

A

Slow to resolve, fungal hyphae present in cytology, deterioration after tx due to massive death of fungus (dramatic PMN response + secondary uveitis)
Surgery: Keratectomy +/- conjunctival flap
Topical: Voriconazole

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11
Q

What is the characteristics and treatment for Immune mediated keratopathy?

A

Only in horses! Insidious onset, no uveitis, low pain, variety in depth
Treatment:
Corticosteroids (only when healed), cyclosporine A or doxycycline, keratectomy (only if superficial), cyclosporine A implant

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12
Q

What is uveitis?

A

Inflammation of the uvea: iris, ciliary body and choroid

Can be anterior or posterior

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13
Q

What are the 3 types of Equine Recurrent uveitis (ERU) ?

A

Active (current episode)
Quiescent (no clinical signs)
Insidious (e.g. appaloosa breeds, constant ERU but low grade clinical signs)

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14
Q

What are some causes of uveitis?

A

Primary/secondary to other eye disease (e.g. ulcer)
Systemic disease (e.g. Rhodococcus)
Leptospira (not so much in UK)
Strong immune mediated component

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15
Q

What are the clinical signs of anterior uveitis?

A

Epiphora (insufficient tear film drainage from the eyes)
Blepharospasm (contraction of eyelid muscles)
Constricted pupil
Chemosis (swelling or oedema of conjunctiva)
Aqueous flare (milky appearance in anterior chamber, blurred iris
Blood (hyphaema), pus (hypopyon) or fibrin in anterior chamber

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16
Q

What are the clinical signs of posterior uveitis?

A

Subtle!
Variable (often mild) pain
Vitritis
Retinal changes

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17
Q

What mydriatic agent should you use in a normal eye exam and why?

A

Tropicamide (lasts 4-6 hours)

NOT Atropine as can cause a normal eye to be dilated for up to 4-6 weeks

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18
Q

What is the medical treatment for uveitis

A

Topical corticosteroid (if no ulcer)
Topical atropine
+/- topical NSAIDs, antimicrobials
Systemic NSAID (flunixin)

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19
Q

What is the reason for using atropine in the treatment of uveitis?

A

Prevents pupil constriction, reduces risk of synechiae (iris stuck to lens)
Helps repair blood ocular barrier

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20
Q

What is the main risk in using atropine to treat uveitis in horses?

A

Risk of colic
Reduces GI motility
(Also box rest is advised which is also a risk factor)

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21
Q

What are the surgical options for uveitis?

A

Cyclosporine A implant (immunomodulatory effect)
Pars plana vitrectomy
Enucleation

22
Q

What is a cataract?

A

Any opacity of the lens

23
Q

Describe the anatomy of the lens

A 
Lens sits behind the iris
Nucleus in centre
Anterior and posterior poles
Suture lines between fibres
Suspended by ciliary bodies
Connected to eye by zonules, provide nutrition
Surrounded by capsule
24
Q

How would you examine for cataracts?

A

Transillumination
Direct focal illumination
Direct beam light at 45 degree angle into the lens
Cataracts appear white

25
Q

What are the 6 types of cataract?

A
  1. Capsular
  2. Nuclear
  3. Perinuclear (lamelar)
  4. Equatorial
  5. Suture (Y shaped)
  6. Complete
26
Q

What is Phacoemulsification?

A

Cataract surgery
An ultrasonic probe is used to break down/emulsify the built up protein of the eye lens that causes cataracts. Once the proteins are broken up, and the lens fragments are removed, an artificial lens is inserted as a replacement
Difficult + high complications in horses!

27
Q

What is glaucoma?

A

Increase intraocular pressure (IOP)

Uncommon in horses, more tolerant of higher pressure

28
Q

What is normal IOP?

A

15-30mm/Hg

29
Q

What produces aqueous humour?

A

Ciliary body

30
Q

How is aqueous humour drained?

A

Drains through iridocorneal and uveoscleral pathways

31
Q

What are the 2 types of glaucoma?

A

Primary –> abnormally developed drainage
Secondary –> damage to drain
(e.g. scarring, debris, vascularization)

32
Q

What are the clinical signs of glaucoma?

A

Hydrophthalmos or buphthalmos (enlarged eye)
Corneal oedema
Corneal striae (folds in Descemet’s membrane)
Lens luxation
Blindness

33
Q

What is lens luxation?

A

Primary –> breakdown of lens zonules (genetic, terriers)

Secondary –> Slipping of the lens due to: Glaucoma, uveitis, neoplasia

34
Q

What is the main problem with lens luxation?

A

If the lens becomes fully detached, it may slip into the anterior chamber of the eye, becoming stuck between the cornea and the iris
Causing acute pain and vision loss

35
Q

What is the medical treatment for glaucoma?

A

Carbonic anhydrase inhibitors
Beta-blockers
NSAIDs and/or corticosteroids
(Prostaglandin derivatives are contraindicated in horses)

36
Q

How should you diagnose glaucoma?

A

Clinical signs
Ultrasound
Tonometry (measure of IOP)

37
Q

What are the surgical options for glaucoma?

A

Laser or chemical destruction of ciliary body
(Chemical - intravitreal gentamicin injection)
Aqueous shunts
Enucleation

38
Q

Describe the anatomy of the fundus

A

Tapetal and non-tapetal regions
Stars of Winslow (involved in blood supply)
Retinal vessels
Optic nerve (oval, salmon pink)

39
Q

Describe the blood supply to the retina

A

Paurangiotic (partially vascularized)

30 to 60 small retinal vessels radiating from optic nerve

40
Q

Describe the layers of the retina

A 
Sclera (white, support layer)
Choroid (red, vascular layer)
RPE (retinal pigmented epithelium, black, absorbs light)
Neurosensory (rods and cones)
Vitreous humour
41
Q

What is an indicator of pathology at the fundus?

A

Pigment accumulation (clumping)

42
Q

What is ERG?

A

Electroretinography(ERG) Testing of the electrical function of the retina, the optic nerve and the central visual pathways
Should be spikes of activity

43
Q

What is topical local anesthetic used in the collection of?

A

Samples for cytology

NEVER for culture and sensitivity

44
Q

What is Rose Bengal Stain used for?

A

Assess tear film quality (if tear film is not well attached to corneal surface = areas of staining)
Assessing margins of neoplasia (SCC)
Fungal ulcers

45
Q

What is the Seidel test?

A

Diagnosis and localisation of penetration of full-thickness ulcers
(All layers of the cornea penetrated + aqueous humor leaking out)
Apply copious fluorescein to eye
Bright green stain where it reacts with the aqueous humour coming from puncture hole

46
Q

What are the 2 nerve blocks commonly performed in a ophthalmic exam?

A

Auriculopalpebral

Frontal

47
Q

Why is nerve blocking used in an ophthalmic exam?

A

Reduces the risk of compromising a fragile eye during forced eyelid opening
E.g. deep corneal ulcer, globe pentrating injury

48
Q

Where does the nasolacrimal duct exit from in the horse?

A

Nasal puncta

Lower end of nose, between the pigmented and non-pigmented area

49
Q

Which ocular reflexes would you use in an ophthalmic exam and when? What nerves do they test?

A

Before sedation!
PLR: Direct + indirect (optic + oculomotor n.)
Dazzle reflex
Menace response: (optic + facial n)
Palpebral reflex: medial and lateral canthus of eye (trigeminal + facial n)
Corneal reflex

50
Q

What is a Finhoff transilluminator used for?

A

Retroillumination
To examine the fundus
Light shone at arms length
Fundic reflection visible through pupil

Equine Studies (15 decks)

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