Ophthalmology Flashcards
Equine eyelashes
Lateral 2/3 upper eyelid
Few/absent lower eyelid
Vibrissae
Dorsomedial to upper eyelid (3-4)
Ventral to lower lid (8-12)
Corpora nigra
Dorsal>ventral
Globe size
H = 48mm
V = 48mm
D = 30mm
Supraorbital fossa
Frontal nerve (CN V)
Anasethesia of upper eyelid
Zygomatic arch
Auriculopalpebral nerve (CN VII)
Akinesia of upper eyelid
Equine fundus
- 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’
Pupillary light reflex
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
Dazzle reflex
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
Slit lamp bio-microscopy
Magnification (x10-x16)
Illumination
Anterior structures (as deep as posterior lens)
Slit
○ Lesion localization
○ Depth of ulceration
Reflections
○ Cornea
○ Anterior lens
○ Posterior lens
Auriculopalpebral nerve block
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
Sensory innervation of the eyelids
Upper eyelid: supraorbital/frontal nerve
Medial canthus: infratrochlear nerve
Lower eyelid: zygomatic nerve
Lateral canthus: lacrimal nerve
Supraorbital (front) nerve block
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Inject 1-2ml through the foramen and then 2-3ml as the needle is withdrawn
Sub-palpebral lavage systems
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
Eyelid lacerations
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
Closure of an eyelid laceration
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)
Corneal disease
Corneal ulceration
○ Simple superficial ulcers
○ Complicated ulcers
○ Viral keratitis
○ Eosinophilic keratitis
Squamous cell carcinoma
Immune-mediated keratitis
Corneal ulceration
Trauma and subsequent infection common
Lacerations
Foreign bodies
Non-healing ulcers
‘Melting’ corneal ulcers
Corneal perforations
Presenting signs of corneal ulceration
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)
Treatment of uncomplicated superficial corneal ulcers
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
Treatment of complicated corneal ulcers
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
Possible surgeries for corneal ulceration
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
Equine herpes virus keratitis
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
Eosinophilic keratitis
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)
