Equine Optho Exam and Orbital Diseases Flashcards
Equine Vision is __ overall vision field with __ degree monocular field and __ binocular field.
Equine Vision is 350 overall vision field with 146 degree monocular field and 65 degree binocular field.
loss of an eye is a significant impact
in your ocular exam from afar, what can you assess?
ocular discharge, eyelash position (down is uncomfortable) and asymmetry or orbital fractures
what parts of your neuro evaluation should be performed before sedation is induced?
- Menace
- Dazzle
- Palpebral
- PLRs (indirect PLR’s is less prominent bc of decussation at the chiasm)
why do you need regional nerve blocks for your optho exam and which 2 are the most common?
The orbicularus oculi muscle is very strong and without a block you may injure the globe. Therefore you should block motor with the auriculopalpebral block and sensory with the supraorbital or frontal block.
Describe the auriculopalpebral block
This is a motor block that primarily blocks the facial nerve effecting the upper eyelid and orbicularis oculi muscle. Use lido/bupiv/mepiv to block on the zygomatic arch caudal to the bony process of the frontal bone. This block will last 1-2 hours
Describe the Supraorbital or Frontal Block
This is a sensory block that blocks the ophthalmic branch of the trigeminal nerve blocking sensation to the central upper eyelid. Its given where the frontal nerve emerges from the supraorbital foramen within the frontal bone.
normal STT and intraocular pressure for a horse
> 20mm/minute and IOP 15-30mmHg
what stain would you use for ulcers v tear film deficiency?
ulcers: fluorescein
tear film deficiency/fungal: rose bengal
what does the jones test do?
Test NLD patency
Irrigation of the NLD
This usually requires sedation and is easiest to perform retrograde from the distal nares to the opening
what should be between the cornea and iris?
nothing, the tyndell effect may pickup particles/granules when a slit beam of light passes through the cornea
upon ophthalmic exam of intra ocular structures the lesions appear dark in __ and white in __
upon ophthalmic exam of intraocular structures the lesions appear dark in retroillumination and white in transillumination
what would you use to dilate the eye 20 minutes prior to examination? how long does it last?
tropicamide and it lasts 4-6 hours
Describe what you should see on a normal fundic exam?
- Optic Disk that is oval, salmon pink and located in the nontapetal fundus
- Retinal vessels, there should be 30-60 small retinal vessels radiating from the optic disk
- Fibrous tapetum, the colors vary but you might see stars of winslow (black dots)
indirect fundoscopy provides a __ field of vision and an __ image
indirect fundoscopy provides a wider field of vision and an inverted image
direct fundoscopy has a __ field of vision and an __ image with most ocular fundi in focus at __
direct fundoscopy has a smaller field of vision and an upright image with most ocular fundi in focus at 0 to -2 D
Briefly describe orbital anatomy
The orbital rim in horses is complete and compromised of the frontal, lacrimal, zygomatic and temporal bones. The orbit also has extraocular muscles that are mostly innervated by the oculomotor (III) n.
a horse presents with a sunken eye appearance, what are 3 possible descriptors?
- Enopthalmos: recession of the globe w/in the orbit
- Microphthalmos: congenitally small globe
- Phthisis bulbi: gradual shrinkage of the globe
enopthalmus
Recession of the globe within the orbit thats usually from loss of orbital contents. Causes include orbital fractures ,resorption of orbital fat, dehydration and sympathetic denervation
Microphthalmia
congenital anomaly resulting in small globe
Phthisis bulbi
Non visual, gradual shrinkage of the globe due to chronic inflammation and low IOP (damage to the ciliary body results in decreased aqueous humor production. If uncomfortable, the eye should be enucleated.
what might be causes/descriptors of a “bulging eye” appearance?
- Buphthalmos: globe is too big
- Exophthalmos: space occupying lesion pushing it forward
Buphthalmos
Enlarged globe associated with chronically increased IOP secondary to glaucoma. It may have other signs suggestive of glaucoma such as corneal edema and Haabs straie. Vision may be present, reduced or absent.
Exophthalmos
Anterior displacement of a normal sized globe caused by a retrobulbar mass, orbital cellulitis, or trauma. If you perform digital retropulsion and there is pain then its inflammation but if its non-painful suspect neoplasia or cystic masses.
Summarize Orbital Fractures
The dorsal orbital rim and zygomatic arch are at the greatest risk for fractures. Its often caused by rearing in confined spaces, kicks to the face and colliding with stationary objects.
how should you treat orbital fractures?
Ensure adequate corneal perfusion and lubrication. Check visual status, and minor non-displaced orbital fractures may not require surgical treatment.
Summarize Orbital fat prolapse
Orbital fat may herniate through weekened episcleral fascia or as a result from trauma. It can be diagnosed by FNA or biopsy and treated by resecting the mass and suturing the conjunctiva surface over the exposed area.
Orbital Cellulitis Clinical Appearance and Causes
Clinical appearance: exophtahlmos, blepharaedema, severe conjunctival swelling, elevated third eyelid, mucoid ocular discharge +/- elevated IOP
Causes: Direct trauma, seeding septic emboli, foreign body, uncontrolled septic endophthalmitis
Diagnosis and Treatment of Orbital Cellulitis
Diagnosis: palpation, sinus percussion, radiographs/US/MRI/CT/FNA and evaluate teeth
Treatment: systemic antimicrobial agents. aggressive NSAIDS, topical lubricants, drainage of abscess, removal of FB, enucleation
Most common types of orbital neoplasia
Neuroendocrine tumors, extra-adrenal paranglioma, nasal and orbital adenocarcinoma, sarcoma, lymphoma, SCC
Diagnosis and Treatment of Orbital Neoplasia
Diagnosis: advanced imaging, orbital ultrasound, FNA, Biopsy
Treatment: Exenteration, Radiation, Chemotherapy, Euthanasia
dorsal v ventral horn of spinal cord
dorsal = sensory
ventral = motor
