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NEU2 > Equine ophthalmology > Flashcards

Equine ophthalmology Flashcards

1
Q

What is blocked by supraorbital nerve blocks in horses?

A

Sensory innervation of the medial half to the medial third of the eye

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2
Q

What is blocked by auriculopalpebral nerve blocks in horses? Purpose?

A

Only motor innervation of upper eyelid. Facilitates examination but not surgery

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3
Q

Describe the method for supraorbital nerve blocks in horses

A
  • Walk needle off supraorbital foramen

- Or insert needle a third of the way along the orbit

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4
Q

Describe the method for the auriculopalpebral nerve block in horses

A
  • Needle inserted in front of the base of the ear at the end of the zygomatic arch, and is introduced until its point lies at the dorsal border of the arch
    Should be able to feel the neurovascular bundle
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5
Q

Describe the method for the lacrimal nerve block in horses

A
  • Use 2-3ml max

- Insert needle subcut just dorsal to lateral canthus, direct medially across dorsal orbital rim during injecion

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6
Q

What is the purpose of lacrimal nerve blocks in horses?

A
  • If ophthalmic exam or eyelid laceration repairs not possible with supraorbital or subpalpebral blocks alone
  • Allows eyelid laceration repair of upper and lower lateral eyelid
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7
Q

Describe the method for infratrochlear nerve blocks in horses

A
  • 2-3ml max
  • Insert needle a medial canthus
  • Direct needle along bony notch on dorsal rim of orbit towards medial canthus
  • Line block method
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8
Q

What is blocked by the infratrochlear nerve block and what is it used for?

A
  • Provides desensitisation of medial eyelid

- Used for third eyelid removal, eyelid laceration repair at medial canthus

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9
Q

Describe the method for the zygomatic nerve block in horses

A
  • Local anaesthetic along ventral and lateral aspect of bony orbit
  • Near junction where eye begins to curve upward
  • Line block on lower part of orbit
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10
Q

What is the zygomatic nerve block used for in horses?

A
  • Blocks remainder of lower eyelid (section not blocked by infratrochlear)
  • Can be used for very painful eyes and opening up lower eyelid
  • Used for lower eyelid laceration repair
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11
Q

When might transpalpebral ultrasound be useful in horses?

A

For corneal oedema, to identify retinal detachment and subluxated lens etc, and therefore establish prognosis

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12
Q

Which probe should be used for transpalpebral ultrasound in horses?

A

10mHz convex

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13
Q

What aspects should be assessed in the ophthalmic aspect of a pre-purchase examination of a horse?

A
  • Evidence of congenital/hereditary ocular disease
  • Current or previous diseases that may lead to decreased vision e.g. uveitis
  • Tumours (SCC, sarcoids)
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14
Q

Describe the appearance of normal corpora nigra in the horses eye

A

Same in both eyes, roughly same size i.e. 3 down 1 up in right eye, should see the same in the left eye

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15
Q

Describe the normal appearance of the equine retina

A
  • Radial blood vessels
  • Tapetal fundus depends on coat colour
  • Non-tapetal fundus contains the optic nerve
  • Optic disc large and salmon pink
  • Slight change in shape at “6 oclock” position is normal
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16
Q

List common conditions that commonly affect the anterior segment of the horses eye

A
  • Fibrin in anterior chamber

- Hypopyon

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17
Q

Describe the cause and treatment of fibrin in the anterior chamber of the horses eye

A
  • Normally secondary to blunt force trauma
  • Treatment: inject tissue plasminogen activator into chamber, within 10 mins get mobilisation of fibrin, another 10 mins and is gone. reduces iris sticking to inside of cornea and less likely to get tissue abnormalities
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18
Q

Describe hypopyon in the horses eye

A
  • Neonates, usually septic
  • Do not use TPA
  • Concurrent uveitis
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19
Q

Identify common conditions affecting the lens of the equine eye

A
  • Cataracts

- Lens luxation/subluxation

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20
Q

Describe congenital cataracts in horses

A
  • Heritable, many breeds affected
  • Most bilateral
  • Can be associated with microphthalmus
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21
Q

Describe the indications for surgery for the treatment of congenital cataracts in horses

A
  • No uveitis
  • Intact retina (PLR, menace and normal on U/S)
  • Vision impairment
  • Appropriate personality of horse as post op topical drugs required
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22
Q

What surgery is used for the treatment of congenital cataracts in horses and what is the prognosis?

A

Phaecoemulsification, good prognosis if <6mo and minimal post-op uveitis

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23
Q

What may cause acquired cataracts in horses?

A
  • Trauma
  • Uveitis
  • Nutritional
  • Occasionally senile cataracts (>20yo)
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24
Q

Describe nuclear lendicular scelrosis of older horses

A
  • Onion rings when look through lens to visualise retina

- Vision usually normal

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25
Q

Discuss the use of surgery in the treatment of acquired cataracts in horses

A
  • Controversial if secondary to uveitis, prone to post-op complications
  • Sight limiting, may wait until bilateral
  • Risk of anaesthetic so wait until bilateral so only one procedure needed
  • ERG and U/S useful for evaluation of retina if perform procedure
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26
Q

What is the cause of lens luxation/subluxation?

A

Trauma

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27
Q

What structures does the uvea consist of?

A
  • Iris
  • Ciliary body
  • Choroid
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28
Q

What is the function of the choroid and where is it located?

A

Provides the blood supply to the retina

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29
Q

Describe the pathogenesis of uveitis in the horse

A
  • Mainly secondary to trauma
  • May be immune mediated due to infectious organisms
  • Systemic lymphoma
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30
Q

List the infectious organisms that may cause uveitis in the horse and identify the most important

A
  • Most important: Leptospira promona/grippotyphosa
  • Toxoplasma
  • Salmonella
  • E. coli
  • Rhodococcus
  • Strongyles
  • Onchocerca
  • EHV-1 and 4
  • EAV
  • EIA
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31
Q

Which breeds are predisposed to equine recurrent uveitis?

A

German WBs, apaloosas, coloured hroses

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32
Q

Describe the presenting signs of uveitis

A
  • Ocular pain
  • Excess lacrimation
  • Blepharospasm
  • Photophobia
  • Miosis
  • Fibrin in anterior chamber
  • Corneal oedema
  • Chorioretinitis
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33
Q

List the irreversible sequelae of uveitis that occur within 24 hours

A
  • Synechiae (anterior or posterior)
  • Iris rests
  • Change in iris pigmentation
  • Reduction in size of corpora nigra
  • Cataracts
  • Retinal detachment
  • Glaucoma
  • Blindness
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34
Q

What are synechiae?

A

Connections that form between either the iris and cornea (anterior) or iris and lens (posterior)

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35
Q

How does retinal detachment occur as a consequence of uveitis?

A

Retina becomes hypoxic due to loss of supply from choroid

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36
Q

Describe the appearance of iris rests and explain how they develop

A
  • Blobs on the iris

- Pupil inflamed, stuck to cornea

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37
Q

What are stretch marks on the eye of a horse indicative of?

A

Glaucomatous, then shrunk down leaving reticulated pattern on surface, often in uveitis

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38
Q

What are the aims of uveitis treatment in the horse?

A
  • Provide analgesia
  • Preserve vision
  • Prevent or minimise recurrence
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39
Q

Outline the aspects of treatment for uveitis in the horse

A
  • Systemic NSAIDs
  • Atropine
  • Corticosteroids
  • Antibiotics
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40
Q

Explain the use of atropine in the treatment of uveitis in the horse

A
  • Topical
  • Dilates pupil, increases drainage angle, reduces pain
  • Decreases pain when miosis is reversed
  • Decreased risk of synechiae and iris rest formation
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41
Q

Discuss the use of corticosteroids in the treatment of uveitis in the horse

A
  • With care, only where not responded to NSAIDs or atropine
  • Never if there is an ulcer
  • May cause an ulcer which can become indolent and difficult to treat
42
Q

Discuss the use of antibiotics in the treatment of uveitis

A
  • Topical and broad spectrum
  • Esp. if using C/Ss
  • Depends on cause of uveitis, generally not required with trauma
43
Q

Outline the prognosis of equine uveitis

A
  • Good with swift and aggressive treatment

- Risk of recurrence

44
Q

What are the future implications of evidence of uveitis in a horses eye?

A

Will be failed at pre-purchase exam

45
Q

Describe the normal appearance of the equine tapetal fundus

A
  • Brown coat: greeny-ble tapetal fundus
  • Chestnuts: yellow fundus
  • Other colours: blue tapetal fundus
  • Bright but not too bright
  • Solid clear line between tapetal and non-tapetal fundus
46
Q

List hereditary disorders of the equine retina

A
  • Retinal colobomas
  • Congenital retinal detachments
  • Chorioretinitis
47
Q

Briefly describe retinal colobomas in horses

A
  • Uncommon
  • Normal optic disc
  • Absence of normal non-tapetal tissue at 6 o’clock
48
Q

What causes congenital chorioretinitis in the horse?

A

EHV-1 in early life (in utero infection) or uveitis

49
Q

Describe the appearance of congenital chorioretinitis in the horse

A
  • Bullet hole lesions in retina (indicative of EHV-1)
  • Hyper-reflectivity of tapetal fundus
  • De- or hyperpigmentation of non-tapetal fundus
  • Retinal/choroidal inflammation manifesting as grey colour
  • Blood loss (hypoxia of retina)
  • Infarction (unusual in the horse)
  • Head trauma
50
Q

Describe the ocular manifestation of equine motor neuron disease

A
  • Retinopathy
  • Retinal pigment epithelial cell accumulation
  • Dark yellow/brown pigment seen as band at elvel of tapetal and non-tapetal fundus junction
51
Q

What may cause retinal detachment in horses?

A
  • Uveitis
  • Trauma
  • Penetrating ocular wounds
52
Q

Describe the appearance of retinal detachment in horses

A
  • Grey lines coming down seen on ophthalmoscopy (outfoldings of retina, out of focus)
  • Multiple lines seen in tapetal reflex
53
Q

What are the 2 main optic nerve disorders in the horse?

A
  • Atrophy

- Ischaemic optic nerve neuropathy

54
Q

List the potential causes of optic nerve atrophy in the horse

A
  • Uveitis
  • Trauma (e.g. head shaking leading to stretching of optic nerve, loss of blood supply)
  • Glaucoma
  • Toxicity
  • Blood loss
55
Q

List the potential causes of ischaemic optic nerve neuropathy in the horse

A
  • Internal carotid occlusion for treatment of guttural pouch mycosis
  • Blood loss
56
Q

What causes vitreitis in horses?

A

Uveitis

57
Q

What may cause vitreal opacity in horses?

A
  • Fibrin

- Porphyrin metabolites (blood)

58
Q

Describe the clinical appearance of vitreitis in horses

A
  • Degeneration of vitreous visible
  • Visible ultrasonographically or whith ophthalmoscope in horses over 20yo
  • Can cause head shaking and reduced vision
59
Q

What are cataracts and traction bands commonly secondary issues to?

A

Vitreitis

60
Q

Describe vitreal floaters (cause, appearance)

A
  • Age change due to break down of products in the vitreous, usually >20yo
  • Secondary to uveitis
  • Can result in headshaking in some horses
61
Q

What chemical methods can be used to facilitate the examination of the front of the equine eye?

A
  • Often sedation with A2a and partial opioid agonist e.g. romifidine and butorphanol
  • Perineural analgesia: supraorbital/corneal nerve blocks, topical analgesia
  • Tetracaine/promethacain
62
Q

List the important considerations in the ocular examination of foals

A
  • Low tear production vs adults
  • Slow PLRs in first 5 days of life
  • No menace for first 2 weeks
  • Hyaloid artery remnants for first few hours, maintained in some
  • Prominent Y shapes on front and back of lens (upside down a back)
  • Reduced corneal sensitivity so trauma more likely and limited signs with ulcers
63
Q

List the samples that can be used in the ophthalmic investigation of the horse

A
  • Swabs
  • Scrapes
  • Biopsy
64
Q

Discuss the use of swabs in the investigation of ocular disease in horses (indications, method)

A
  • Indications: rapidly progressive, deep ulcers, treatment failure
  • Otherwise, limited use
  • Superficial bacterial sampling for culture and sensitivity
65
Q

Describe the method for the swabbing of melting ulcers

A
  • Take sample

- Roll sample onto slide then send to lab, otherwise material ends up in storage medium and not on swab

66
Q

What is the main indication for the use of scrapes in the investigation of ocular disease in horses?

A

Suspicion of bacterial (superficial) or fungal (descemets membrane) disease

67
Q

Outline the method for scrape sampling of the eye in horses

A
  • Use small pair of ophthalmic forceps and scissors
  • Cut around edge of ulcers
  • Perform squash preparations to look for bacterial disease and fungal disease
68
Q

What is the main indication for the use of biopsy in the investigation of ocular disease in horses?

A

Suspicion of fungal or viral/immune mediated disease

69
Q

Evaluate the use of flurescein staining in the investigation of ocular disease in horses (advantages and disadvantages)

A
  • Stains the corneal stroma
  • Advantage: confirms epithelial defect/ulcer
  • Disadvantage: may not identify early fungal disease, ulcers penetrating into the basement membrane will not stain
70
Q

Evaluate the use of Rose bengal staining in the investigation of ocular disease in horses

A
  • No longer available
  • Identifies defects in pre-corneal tear film
  • Identifies mucin defects in early fungal disease
  • use in acutely painful eye
71
Q

How can tonometry be performed in the horse?

A
  • Manually (fingers)

- Digital tonometer

72
Q

List diseases of the eyelids, third eyelid, cornea and aqueous of the equine eye and identify those that are common

A
  • Eyelid injury and entropion (common)
  • Congenital abnormalities
  • Eyelid neoplasia (sarcoids, melanoma and SCC all common)
  • Habronema
  • Ulcerative keratitis (common): bacterial common, keratomycosis (fungal, common), other e.g. eosinophilic
  • Varial keratitis (non-ulcerative/punctate keratitis, common)
  • Glaucoma (common)
  • Dentigerous cysts (rare)
73
Q

List the common types of ocular diseases in foals

A
  • Corneal ulcers
  • Uveitis
  • Congenital abnormalities
  • Entropion
74
Q

List the potential ocular congenital abnormalities seen in foals

A
  • Microphthalmos
  • Persistent pupillary membranes
  • Congenital cataracts
  • Congenital glaucoma
  • Dermoids, lacrimal punctae agenesis
75
Q

What causes entropion in foals? Explain

A

Frequently a secondary abnormality due to dehydration or emaciation causing loss of elasticity of skin. Can also be congenital/secondary

76
Q

Describe the treatment of entropion in foals

A
  • Stain for ulcers (clinical signs not obvious)
  • Placement of horizontal mattress sutures to correct
  • Avoid injection of emulsion based substances as these lead to bleeding, inflammation
77
Q

Describe the treatment of eyelid lacerations in horses

A
  • Sutures placed, can heal easily
  • Need to act as soon as possible to avoid corneal injury and scarring
  • Avoid excessive debridement even if looks avascular as need to be able to appose wound edges
  • Ensure no suture material passes through conjunctiva onto conrea
  • 2 layer closure with smallest material possible
78
Q

Describe the treatment of eyelid melanomas in horses

A
  • Excision, lid resonstruction, cryotherapy
  • Enucleation
  • Difficult to manage if very big
79
Q

Describe the treatment of eyelid sarcoids in horses

A
  • Topical brachytherapy Iridium wires (98% success)
  • Intralesion therapy with BCG (100% non recur) +/- debulking +/- 5-GU (not currently available)
  • Surgical excision (50% non-recur)
  • 5-FU alone (67% non recur)
80
Q

Describe the pathogenesis of eyelid squamous cell carcinoma in horses

A
  • UV light exposure on unpigmented skin
  • Increases with age
  • Appaloosa predisposed
81
Q

Which part of the eye is commonly affected with SCCs in horses? Treatment and consequences?

A
  • Commonly third eyelid
  • Easily removed with local blocks, sedation and performed standing
  • May lead to spread to other parts of eye e.g. limbus
82
Q

Outline the prognosis and treatment for SCCs affecting the limbus of horses

A
  • Poor prognosis

- GA required for debulking

83
Q

What are the main differentials for ocular SCCs in horses?

A

Other neoplasms or parasitic

84
Q

Discuss the long term prognosis of ocular squamous cell carcinoma in horses

A
  • Rarely metastatic (except limbic form)
  • High long term recurrence (same or other eye)
  • Often require multiple therapies
85
Q

Outline the treatment options for ocular SCCs

A
  • Surgical excision (50% non recur)
  • Immunotherapy BCG (unknown efficacy)
  • Chemotherapy with cisplatin (70% non recur, also mitomycine)
  • Cryotherapy (50-100% non recur)
  • Brachytherapy iridium (90% non recur)
86
Q

Describe the appearance of ocular habronemiasis in horses

A
  • Granulomatous lesions
  • May be bilateral
  • Blepharitis
  • Often associated with granuloma in medial canthus
87
Q

Describe the pathogenesis of habronemiasis in horses

A
  • Fly lays eggs in mucocutaneous junctions esp. if have ocular or nasal discharge
  • Inflammatory response to larvae that leads to granulomas e.g. at medial canthus (aka summer sores of mouth and nose)
  • Worms incredibly pruritic once inflammation set up
88
Q

Describe the treatment and control of habronemiasis in horses

A
  • Ivermectin (weekly for 4 weeks)
  • Systemic NSAIDs
  • Fly control important
  • May see inflammatory increase before improvement following starting treatment
89
Q

Explain how melting ulcers develop in the horses eye

A
  • Proteinases within PCTF
  • Normal defence/repear mechansims of PMD, epithelial cells and stromal fibroblasts
  • Production stimulated by bacteria (commonly Peudomonas) and fungi
  • Proteinases produces by some bacteria directly
  • Collagenases produced by some pathogens
90
Q

Describe the appearance of melting ulcers in horses eyes

A

Grey liquefying appearance at edge of ulcer

91
Q

List the common pathogens of the equine cornea

A
  • Staphylococcus
  • Streptococcus
  • Pseudomonas
  • Aspergillus
  • Fusarium
  • EHV
92
Q

Describe the clinical signs of corneal ulcers in horses

A
  • Blepharospasm
  • Epiphora
  • Photophobia
  • Mild drooping of eyelids
93
Q

Identify the main elements in the treatment of corneal ulcers in horses

A
  • Prompt aggressive treatment
  • Consider infection in all ulcers
  • Concurrent uveitis should be addressed (NSAIDs, atropine)
  • Fungal disease (less common in UK)
94
Q

List the most common causes of fungal corneal ulceration in horses

A
  • Most common in hot, humid countries
  • Plant material
  • Not improved following long term antibiotic
  • Prolonged corticosteroids
95
Q

Describe the medical treatment of simple ulcers in horses

A
  • Broad spec topical antibiotics
  • Chloramphenicol
  • Fusidic acid for G+ve, but irritant and not tolerated for more than a few applications
  • Triple antibiotic: neomycin, gramicidin, polymyxin B
96
Q

Describe the medical treatment of melting ulcers

A
  • Likely to involve Pseudomonas, ciprofloxacin used (resistance to gentamicin)
  • Fluoroquinolones (culture and sensitivity would take too long to get back so in this scenario FQs ok)
  • Otherwise enucleate eye
  • Chloramphenicol, polymyxin B
  • Cephalosporins for beta-haemolytic Streptococci
97
Q

List the methods for control of melting ulcers (other than antibiotics) in horses

A
  • Aim to block collagenase activity of Pseudomonas, beta-haemolytic Streptococci or fungi
  • Plasma (horse’s own) or serum (plasma better)
  • EDTA
  • Acetyle cysteine
  • Can combine 2 or 3 for severe ulcers
  • Consider hourly medication for first 12-24 hours, may need hospitalisation
98
Q

Explain the use of plasma or serum in the control of melting ulcers in horses

A
  • As often as possible, make fresh every 5 days,

- Has anti-proteinase activity

99
Q

Describe and explain the use of EDTA in the control of melting ulcers in horses

A
  • Add sterile saline to blood tube to make EDTA solution, plus distilled water into eye
  • Binds calcium and other metals that bacteria and fungi use for growth, thus inhibiting growth
  • Cannot use EDTA and plasma together as EDTA will react with blood proteins, rather than binding out the metals
100
Q

Describe the pathogenesis of fungal ulcers in horses

A
  • Usually colonisation of ulcer with commensal fungi
  • Proteinase release
  • Anti-angiogenic
  • Affinity for descemets membrane

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