Diseases of the Globe Flashcards
The overall visual field of the horse is:
350 degrees
The horse can see ______ degrees with monocular vision, and _____ degrees with binocular vision
145 degrees
65 degrees
Before any sedation is induced, you should evaluate:
Cranial nerves
Which cranial nerve reflexes are commonly assessed in horses?
Menace response
Dazzle reflex
Palpebral reflex
PLRs
Which ocular muscle is very strong in horses, often requiring orbital nerve blocks for a proper ophthalmic exam?
Orbicularis oculi
Which ocular nerve blocks in horses block the motor and sensory function of the eye?
Auriculopalpebral (motor)
Supraorbital or frontal (sensory)
For ocular nerve blocks, what size needle is used and what volume/choice of anesthetic?
25 gauge needle
1-2 mL
Lidocaine, bupivacaine, or mepivacaine
What are the landmarks for an auriculopalpebral nerve block?
On the zygomatic arch, caudal to the bony process of the frontal bone
What are the landmarks for an supraorbital nerve block?
Palpation of the supraorbital foramen
*Thumb: below dorsal orbital rim
*Middle finger: supraorbital fossa
*Index finger: straight down midway between other two fingers
Supraorbital nerve block desensitizes:
Sensation to central upper eyelid
Blocks the ophthalmic branch of Trigeminal nerve
Auriculopalpebral nerve block stops motor output from:
Orbicularis oculi muscle, mostly upper eyelid
Blocks palpebral branch of auriculopalpebral nerve (Facial nerve)
Tear production in horses should be:
> 20mm/min
IOP in horses should be:
15-30mmHg
What would give indication for irrigation of nasolacrimal duct?
Epiphora, mucoid ocular discharge, nasal puncta diacharge
Describe the process of flushing the NLD retrograde:
- Start at distal nares opening
- 5 or 6 polyethylene urinary catheter
- 12 to 20 mL syringe with sterile eyewash +/- fluoroscein stain
Describe the process of flushing the NLD normograde:
- Start at proximal eyelid puncta (lower eyelid puncta usually larger)
- 8 to 20g IV Cannula
- Excessive force can damage NLD
What drug is commonly used to dilate the pupil of horses for a complete ophthalmic exam?
1% Tropicamide
(done ~20 minutes prior to exam)
*lasts 4-6 hours
The optic disc should appear:
Oval, salmon-pink, in the non-tapetal fundus
The equine fundus is unique because:
Tapetum is fibrous (Stars of Winslow)
Indirect fundoscopy produces:
Inverted and reversed image
A sunken appearance to the globe has 3 likely etiologies, including:
Enophthalmos
Microphthalmos
Phthisis bulbi
Enophthalmos is defined as:
Recession of the globe; usually secondary to loss of orbital contents
Causes of enophthalmos (4)?
- Orbital fractures
- Resorption of orbital fat
- Dehydration in foals (entropion)
- Sympathetic denervation (Horner’s Syndrome)
Microphthalmia is defined as:
Congenital anomaly resulting in a small globe
