Equine Ophthalmology Flashcards
Granula iridica
- what is it
- function
- pigmented, cystic vascular
remnants of the embryonic
optic vesicle.
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Functions: - reducing sunlight-induced
glare - form at least 2 small visual
‘pinhole’ pupils (one lateral
and one nasal) to increase
visual clarity in daylight
unique anatomy of equine fundus
- Stars of Winslow (end-on vessels)
- Paurangiotic retinal vasculature
Nerve Blocks for equine eye, functions of nerves
- why we need this?
- Frontal Nerve Block
* Br of CN Vo (Sensory)
* Supraorbital foramen - Auriculopalpebral Nerve Block
* Br of CN VII
* Motor to orbicularis oculi m.
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Horses have eyelids like a vice-grip!
> not an accurate tear measurement without - fight against lids = increased pressure
Frontal Nerve Block - placement, drug
supraorbital foramen > find borders of supraorbital process
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2 ml lidocaine
* 25 ga needle, 5/8”
* Subcutaneously and perpendicular to
the bone (not INTO the foramen)
Auriculopalpebral Block
- placement, drug
Method 1:
* Strum the nerve by running finger down the
dorsal aspect of the zygomatic arch near the
temporal bone
* 25 ga needle, 5/8”
* place subcutaneously perpendicular to the
bone
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Method 2:
* Jcn of zygomatic arch and caudal border of ramus
* Cannot feel nerve
* 25 ga needle to hub
* 2-3 ml lidocaine
Ocular Examination, considerations
- Ocular exam sheet a necessity
- Sedation – lowers the head, safer
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Evaluation of the head and lids - Symmetry
- Trauma
- Globe position
- Globe size
- Eyelid position
- Discharge
- Third eyelid
- Direction of the eyelashes
Neuro-ophthalmic examination
- Dazzle reflex (CN II, VII)
- Menace response (CN II, VII, cortex) – learned response (2 weeks)
- Pupillary light reflex (CN II, III) – check in bright and dim room
> Anisocoria – check at 2-3 feet away
> Direct
> Consensual (easier to check with 2 people, slower than a dog/cat)
Fundic examination
- how to, what to look for?
- Dilate using tropicamide
- Paurangiotic retinal vasculature
- Stars of Winslow = end-on vessels
Nasolacrimal system
- assessment
- flushing?
- Jones test = passive flow
<><> - Cannulation and flushing
- Retrograde (= nose to eye) > usually do this one
- Normograde (= eye to nose)
- 3 Fr catheter
- Topical anesthesia / local gel anesthesia
Neonatal ophthalmology
Particularities
- At birth: pupil is almost round until day 3-5 of age
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Neuro-ophthalmology - Absent menace response until 2 weeks of age (this is much earlier than in predators), can be asymmetric
- Reduced PLR, especially if excited
- Strabismus in foals less than 4 weeks of age (ventromedial angle)
Neonatal ophthalmology
Microphthalmia (small and blind)
- significance?
- what should we do?
- Moderate-severe blind
- Mild: other intraocular abnormalities
- Entropion in mild to moderate cases
- Unilateral or bilateral (often just one)
- Enucleation if blind
Neonatal ophthalmology
- Subconjunctival hemorrhages
- significance? where? do we do anything?
- Superior nasal bulbar conjunctiva
- Free margin of third eyelid
- Resolve by 14 days
Neonatal ophthalmology
Entropion
- who gets this?
- secondary issues?
- progression? what should we do?
- Premature, sick, dehydrate foals
- Can have secondary corneal ulceration
- Entropion is temporary in most cases
> Temporary tacking sutures - If persists after tacking sutures,
> Hotz-Celsus (rarely needed)
Neonatal ophthalmology
Atresia of nasolacrimal system
- where?
- how to detect?
- what we do?
- Commonly found at nasal punctum
- Normograde flush to see the conjunctiva overlying the location of the punctum bulge
- Contrast imaging if no bulge is noted (absent duct?)
<><> - Surgical correction:
- Snip away conjunctival tissue overlying the
bulge - Placement of catheter for several weeks-months to prevent healing conjunctiva from re-covering the nasal punctum
Neonatal ophthalmology
Persistent Pupillary Membranes
- appearance, where they arise?
- iris tissue arising from iris collarette
- Iris to iris
- Iris to cornea: leukoma or corneal scar
- Iris to lens: anterior capsular cataract
