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Equine michaelmas 23 > Ophthalmology > Flashcards

Ophthalmology Flashcards

1
Q

Equine eyelashes

A

Lateral 2/3 upper eyelid
Few/absent lower eyelid

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2
Q

Vibrissae

A

Dorsomedial to upper eyelid (3-4)
Ventral to lower lid (8-12)

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3
Q

Corpora nigra

A

Dorsal>ventral

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4
Q

Globe size

A

H = 48mm
V = 48mm
D = 30mm

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5
Q

Supraorbital fossa

A

Frontal nerve (CN V)
Anasethesia of upper eyelid

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6
Q

Zygomatic arch

A

Auriculopalpebral nerve (CN VII)
Akinesia of upper eyelid

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7
Q

Equine fundus

A
  • Paurangiotic
    • Few vessels at 6 o’clock
    • Salmon pink ONH
    • Dorsal fibrous tapetum
      ○ Colour variation
    • Non-tapetal area
      ○ Usually dark brown
    • End on choroidal capillaries
      ○ ‘Stars of Winslow’
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8
Q

Pupillary light reflex

A

Light directed in each eye in turn

Direct and consensual response

Consensual is weak in horse

75% decussation at optic chiasm

Afferent = CN II (optic)

Efferent = CN III (oculomotor)

Does not involve visual cortex

Not a test of vision

Useful test of retinal function

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9
Q

Dazzle reflex

A

A very bright focal light source

Eyelid closure

Afferent = CN II (optic)

Efferent = CN VII (facial)

Subcortical reflex

Not a test of vision

Useful test of retinal function

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10
Q

Slit lamp bio-microscopy

A

Magnification (x10-x16)

Illumination

Anterior structures (as deep as posterior lens)

Slit
○ Lesion localization
○ Depth of ulceration

Reflections
○ Cornea
○ Anterior lens
○ Posterior lens

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11
Q

Auriculopalpebral nerve block

A

Auriculopalpebral nerve = branch of facial nerve (VII)

Motor supply to upper eyelid

Facilitates eye examination and standing procedures

Crosses bone anterior to highest part of zygomatic arch

Can be ‘strummed’

Inject 3-5ml mepivacaine subcutaneously

5/8” 23 or 25G needed

Eyelid becomes droopy and floppy

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12
Q

Sensory innervation of the eyelids

A

Upper eyelid: supraorbital/frontal nerve

Medial canthus: infratrochlear nerve

Lower eyelid: zygomatic nerve

Lateral canthus: lacrimal nerve

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13
Q

Supraorbital (front) nerve block

A

Sensory innervation to upper eyelid

Can feel supraorbital foramen as depression in zygomatic arch

1/2” deep into supraorbital foramen

Inject 1-2ml through the foramen and then 2-3ml as the needle is withdrawn

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14
Q

Sub-palpebral lavage systems

A

Frequent topical medications

Head-shy horses

Follow drug with air bolus

Indusion pumps

Footplate under upper or lower eyelid

Connected to silicone tubing

Sutured in place to skin

Tied to mane

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15
Q

Eyelid lacerations

A

Common box and field injuries
○ Blunt trauma - laceration with swelling
○ Trauma on sharp objects - straight laceration
○ Ripping injuries - starting at lateral canthus

Acute and readily noticed by owner

Important to examine whole eye
○ Corneal injury?
○ Uveitis?
○ Lens penetration?

Excellent blood supply

Good prognosis with surgical repair

Hanging fragments should not be excised

PRESERVE THE EYELID MARGIN

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16
Q

Closure of an eyelid laceration

A

Closure in TWO layers with magnification (at least 2.5X)
○ Deep subconjuctival layer
§ First
§ Simple continuous
§ 5/0 - 6/0 polyglactin 910

○ Skin layer
§ Appose eyelid margin first with figure of 8 or mattress suture
§ Simple interrupted
§ 4/0 - 6/0 non-absorbable sutures (absorbable can be used)

17
Q

Corneal disease

A

Corneal ulceration
○ Simple superficial ulcers
○ Complicated ulcers
○ Viral keratitis
○ Eosinophilic keratitis

Squamous cell carcinoma

Immune-mediated keratitis

18
Q

Corneal ulceration

A

Trauma and subsequent infection common

Lacerations

Foreign bodies

Non-healing ulcers

‘Melting’ corneal ulcers

Corneal perforations

19
Q

Presenting signs of corneal ulceration

A

Non-specific signs of pain
□ Blepharospasm
□ Photophobia
□ Epiphora

Uveitis signs (antidromic reflex via trigeminal stimulation)
□ Miosis
□ Aqueous flare
□ Hypopyon

Corneal signs
□ Loss of epithelium and/or stroma
□ Corneal vascularisation
□ Keratomalacia (corneal melting)

20
Q

Treatment of uncomplicated superficial corneal ulcers

A

Epithelial loss only with no evidence of infection

Topical broad-spectrum antibiotic
□ Bacteriostatic - suitable for prophylaxis
□ Chloramphenicol

Treat reflex uveitis
□ Atropine sulphate 1%
□ Mydriatic and cycloplegic
□ To effect
□ 2-4x daily

Systemic analgesia (NSAID)
□ Flunixin meglumine
□ Phenylbutazone

21
Q

Treatment of complicated corneal ulcers

A

Antibiotics
□ Broad spectrum with good Gram negative cover
□ Bactericidal
□ Ofloxacin, ciprofloxacin (fluoroquinolones)

Anti-collagenase
□ Homologous serum

Both every 2-4 hours initially

Atropine and NSAID

May need surgery

22
Q

Possible surgeries for corneal ulceration

A

Keratoplasty (‘grafting’)
- For deep and melting corneal ulcers
- Provide tectonic support +/- blood supply

Combine with keratectomy to remove infected tissue (e.g. fungal keratitis)

Numerous techniques and grafting materials

Conjunctival pedicle graft

23
Q

Equine herpes virus keratitis

A

EHV-2

Multifocal, white epithelial opacities
§ Punctate, dendritic, or lace like

May be ulcerative (fluorescein positive) or non-ulcerative

Diagnosis
§ Clinical appearance
§ PCR testing

50% horses PCR +ve without clinical signs!

Specific treatment
§ Topical antivirals (ganciclovir)

Recurrence possible

24
Q

Eosinophilic keratitis

A

Immune mediated disease

Variable appearance

Level of discomfort varies

Corneal ulceration associated with creamy white necrotic plaques

Cytology is diagnostic (eosinophils)

Infectious causes must be ruled out

Specific treatment
§ Topical corticosteroids
§ Prolonged treatment may be required (months)

25
Q

Squamous cell carcinoma

A

Most common neoplasia of equine eye

Eyelids, conjunctiva, cornea, orbit

Diagnosis via cytology/histopathology

Treatment
○ Surgical excision/debulking
○ Adjunctive therapy
§ Cryotherapy
§ Radiofrequency hyperthermia
§ Beta irradiation (strontium)

26
Q

Immune mediated keratitis

A

Fairly common

Can affect all layers of cornea (epithelium, stroma, endothelium)

Uveitis not a feature (normal intraocular pressure)

Relatively non-painful

Patches of thickened epithelium

Stromal fibrovascularisation

Corneal oedema (may be profound)

Usually unilateral, may be bilateral

Treatment
○ Topical corticosteroids QID
○ Topical ciclosporin BID/TID
○ Superficial keratectomy?

27
Q

Equine recurrent uveitis

A

Most common cause of blindness in horses

Episodes of intraocular inflammation weeks to months after initial uveitis episode

Bilateral or unilateral

Any age, most horses 4-8 years of age

Immune-mediated disease

Associated with infectious agents - Leptospira spp.

Association with systemic disease

Diagnosed on clinical signs and history (?Leptospira serology)

Classified according to location of inflammation
○ Anterior uveitis (iris, ciliary body, anterior chamber)
○ Posterior uveitis (vitreous, retina, choroid)
○ Panuveitis (all areas of uveal tract)

Presentation varies with stage of chronicity

Varying levels of visual deficits

28
Q

Acute recurrent uveitis

A

Pain, lacrimation, blepharospasm

Eyelid oedema

Perilimbal corneal vascularisation

MIOSIS

Some corpora nigra loss

Inflammatory debris within anterior chamber
§ Fibrin
§ Keratic precipitates (inflammatory debris on corneal endothelium)
§ Hypopyon

Vitritis

Hypotony (low intraocular pressure)

29
Q

Chronic recurrent uveitis

A

Less pain

Darkened iris

Corneal oedema

Adhesions between iris and lens (posterior synechiae)

Corpora nigra atrophy

Corneal mineralisation (calcific band keratopathy)

Cataract

Lens luxation/subluxation

Chorioretinal scarring

Glaucoma

End-stage - small shrunken globe (phthisis bulbi)

30
Q

Chorioretinal scarring in recurrent uveitis

A

Often peripapillary

Bullet holes

“Butterfly lesions”

Previous inflammation

Effect on vision?

Assessment of blood vessels

31
Q

Treatment of reccurent equine uveitis

A

Anti-inflammatories
§ Topical
□ Corticosteroids (e.g. prednisolone acetate)
□ NSAIDs (e.g. bromfenac)
§ Systemic NSAIDs
□ Flunixin
□ Phenylbutazone

Atropine
§ Mydriatic
§ To effect
§ 4-6x daily initially

Suprachoroidal ciclosporin implants

Equine michaelmas 23 (17 decks)

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